JP6994736B2 - A method for manufacturing an electrolyte for a solid oxide fuel cell. - Google Patents

Description

The present invention relates to a method for producing an electrolyte for a solid oxide fuel cell, and more specifically, an electrolyte for a solid oxide fuel cell having a gas blocking property and capable of forming a smooth and thin electrolyte. Regarding the manufacturing method.

The solid oxide fuel cell has a structure in which an electrolyte is sandwiched between a fuel electrode and an air electrode. The fuel electrode is required to have high electron conductivity and gas diffusivity, and for example, a porous body such as yttria-stabilized zirconia (YSZ) is used.

The electrolyte plays a role of conducting oxygen ions from the air electrode to the fuel electrode, and while high ionic conductivity is required, gas blocking property and electron insulating property are required.

The electrolyte layer is thinned to improve the ionic conductivity and the performance of the solid oxide fuel cell is improved, and the surface thereof is preferably smooth in order to prevent the strength of the electrolyte layer from decreasing.

However, the fuel electrode in contact with the electrolyte is a porous body having irregularities on the surface, and in particular, a thin and flat electrolyte layer having large pores, for example, a surface roughness Rz of 4 μm or more and a rough surface on the rough fuel electrode. Is difficult to form.

In Japanese Patent Application Laid-Open No. 2005-158641 of Patent Document 1, a porous electrode base material is impregnated with a resin to close pores and polished, and an electrolyte is formed on the porous electrode base material and then fired. It is disclosed that an electrolyte membrane having a uniform film thickness can be formed by removing the resin.

Japanese Unexamined Patent Publication No. 2005-158641

However, in the method for forming an electrolyte described in Patent Document 1, the contact area between the electrolyte and the fuel electrode is small and peeling is likely to occur. In addition, mirror polishing is required, which increases man-hours and lengthens the cycle time. Further, in the fuel cell, the resin may remain on the porous electrode base material and the reactivity of the electrode may decrease.

The present invention has been made in view of the problems of the prior art, and an object of the present invention is to provide a method for producing an electrolyte for a solid oxide fuel cell capable of forming a thin and smooth electrolyte. There is something in it.

As a result of diligent studies to achieve the above object, the present inventor has arranged a porous fuel electrode (hereinafter referred to as a porous anode layer) on a smooth surface, and with an electrolyte via the porous anode layer. It has been found that the above-mentioned problems can be solved by flowing the metal ion solution to the smooth surface, heating and firing, and the present invention has been completed.

That is, in the method for producing an electrolyte for a solid oxide fuel cell of the present invention, a filling step of filling the pores of the porous anode layer with a metal ion solution and heating of the porous anode layer filled with the metal ion solution are performed. It also comprises a heating step of forming a solid electrolyte.
The filling step is characterized in that the pores opened on one surface side of the porous anode layer are closed with the metal ion solution and a smooth surface of the metal ion solution is formed.

According to the present invention, the metal ion solution forming the electrolyte by firing is allowed to flow down to the smoothing member via the porous anode layer arranged on the smoothing member, so that the metal ion solution is under the porous anode layer. It is possible to close the pores on the side and wet the surface of the smoothing member to form a smooth thin electrolyte film.

It is a schematic diagram explaining the filling process of this invention. It is a schematic diagram explaining another filling process of this invention. 6 is a surface SEM image of the porous anode layer used in Examples and Comparative Examples. 6 is a surface SEM image of the solid electrolyte layer of Example 1. It is a diffraction pattern of the composite oxide forming the solid electrolyte layer. 6 is a surface SEM image of the solid electrolyte layer of Example 2. 3 is a surface SEM image of the solid electrolyte layer of Example 3. 6 is a surface SEM image of the solid electrolyte layer of Example 4. 6 is a surface SEM image of the solid electrolyte layer of Example 5. 6 is a surface SEM image of the solid electrolyte layer of Example 6. It is a cross-sectional SEM image of a porous anode layer. 6 is a cross-sectional SEM image of the solid electrolyte layer of Example 6. It is a surface SEM image of the solid electrolyte layer of Comparative Example 1.

The method for producing the electrolyte for a solid oxide fuel cell of the present invention will be described in detail.
The above-mentioned method for producing an electrolyte uses a metal ion solution containing metal ions as a composite oxide that forms a solid electrolyte layer (hereinafter, may be simply referred to as “electrolyte layer”) by firing.

Then, a filling step of filling the pores of the porous anode layer with the metal ion solution and a heating step of heating the porous anode layer filled with the metal ion solution to form a solid electrolyte are provided.

In the filling step, at least the pores opened on one surface side of the porous anode layer are closed with the metal ion solution, and a smooth surface is formed on one surface side of the porous anode layer with the metal ion solution. It is a process.

Specifically, as shown in FIG. 1, the porous anode layer 1 is arranged on the horizontal smoothing member 2, and the above the porous anode layer, that is, from the other surface side, the smoothing member side, that is, The metal ion solution 3 is allowed to flow down through the porous anode layer 1 toward one surface side of the porous anode layer.

Then, the metal ion solution 3 passes through the porous anode layer 1 and accumulates in the pores 11 that open on one surface of the porous anode layer in contact with the smoothing member. The metal ion solution 3 enters the contact portion 12 between the porous anode layer 1 and the smoothing member 2, and spreads wet on the surface of the smoothing member 2 to cover the surface of the porous anode layer 1.

Then, by drying the metal ion solution 3 while keeping the smoothing member 2 horizontal to eliminate the fluidity and fixing the metal ion solution 3, a thin and smooth film containing the metal ions is formed. By calcining the membrane containing the metal ions in the heating step, a thin electrolyte having a smooth surface can be formed.

If the surface unevenness of the porous anode layer is large, the metal ion solution does not necessarily have to pass through the inside of the porous anode layer, and even if the metal ion solution is transmitted along the surface of the smoothing member and filled in the pores of the porous anode layer. good.

The heating temperature in the heating step depends on the metal ion solution and the porous anode layer, but is preferably 300 ° C. or higher and 700 ° C. or lower, and preferably 350 ° C. or higher and 450 ° C. or lower.

By heating in the above temperature range, the effect on the porous anode layer is small, and components other than metal ions in the metal ion solution described later are decomposed and eliminated, and the metal ions in the metal ion solution are oxidized. Can form an electrolyte layer.

In the production method of the present invention, the heating step may be performed immediately after the filling step, but a drying step may be provided before the heating step to dry the metal ion solution filled in the pores.

By providing the drying step, the film containing metal ions is fixed to the porous anode layer, and even if the porous anode layer is separated from the smoothing member, the shape change of the film containing metal ions is prevented, so that the smoothing member and the porous member are porous. It is not necessary to heat and fire the quality anode layer as a unit, which increases the degree of freedom in the heating process.

If the porous anode layer is lifted without drying the metal ion solution and the smooth member is separated from the metal ion solution, the surface of the metal ion solution becomes uneven and the smooth surface is formed. Cannot be formed.

That is, whether or not the metal ion solution stays in the pores of the porous anode layer when the metal ion solution accumulated in the pores of the porous anode layer separates from the smoothing member is the surface tension of the metal ion solution. It depends on the balance between viscosity and gravity.

Therefore, in pores with a large opening diameter, the surface tension of the metal ion solution becomes smaller than gravity, causing dripping to form convex portions, and in pores with a small opening diameter, the surface tension of the metal ion solution is greater than gravity. As the size increases, the lower end of the metal ion solution enters the pores to form recesses, so that the surface unevenness becomes large.

In the present invention, the smooth surface of the electrolyte means that the surface roughness Rz is 200 nm or less.

The smoothing member is wetted with the metal ion solution, does not react with the metal ion solution or the porous anode layer in the heating step, and is separated from the formed electrolyte layer without being decomposed or melted by itself. If it is a thing, there is no particular limitation.

For example, a silicon wafer having an oxide film formed on its surface is an ultra-flat and ultra-clean substrate whose surface is mirror-polished to eliminate fine irregularities and fine particles to the limit, and has excellent heat resistance. , Can be preferably used.

The amount of the metal ion solution flowing down in the filling step is preferably an amount such that the film thickness of the electrolyte layer formed in the porous anode layer is 0.5 μm or more.
When the film thickness of the electrolyte layer formed in the porous anode layer is 0.5 μm or more, the separation between the electrolyte and the fuel electrode is prevented and the gas barrier property is improved.

The upper limit of the thickness of the electrolyte layer formed in the porous anode layer is preferably 1/5 or less, more preferably 1/10 or less, and further 1/15 of the film thickness of the porous anode layer. The following is preferable. Specifically, it is preferably 2 μm or less, although it depends on the film thickness of the porous anode layer.

Next, the metal ion solution will be described.
The metal ion solution is an aqueous solution in which a metal forming a composite metal oxide exhibiting oxygen ion conductivity is dissolved by firing, and contains ions of at least two kinds of metals selected from the group consisting of transition metals.

Examples of the oxide forming the composite metal oxide include ceria (CeO ₂ ), yttrium (Y ₂ O ₃ ), gadrine (Gd ₂ O ₃ ), zirconia (ZrO ₂ ), and scandia (Sc ₂ O ₃ ). , Calcia (CaO), magnesia (MgO), and Samaria (Sm ₂ O ₃ ).
Among them, a composite metal oxide containing two or more selected from the group consisting of ceria (CeO ₂ ), yttrium (Y ₂ O ₃ ), gadolinia (Gd ₂ O ₃ ) and zirconia (ZrO ₂ ) can be preferably used. ..

The metal ion solution may flow down the porous anode layer without reacting with the porous anode layer, and may be a chelate complex in which a ligand is coordinated with the ion of the metal, or a nitrate or sulfate of the metal. An aqueous solution in which acetate, citrate, tartrate acid, and malic acid are dissolved can be used.
Among them, since the chelate complex is very stable in an aqueous solvent, it is not affected by the pH of the aqueous solution, coexisting ions, and the addition of additives such as surfactants and viscosity modifiers, so that the degree of freedom in solution adjustment is high. Even if it remains in the porous anode layer, the chelate component is thermally decomposed by firing and easily discharged to the outside of the porous anode layer, so that it can be preferably used.

The chelating agent that forms the chelate complex is not particularly limited as long as it can stably capture the metal ions of the metal.

Examples of the chelating agent include ethylenediaminetetraacetic acid, 1,2-cyclohexanediaminetetraacetic acid, dihydroxyethylglycine, diaminopropanol tetraacetic acid, diethylenetriaminepentaacetic acid, ethylenediaminediacetate, ethylenediaminedipropionic acid, hydroxyethylenediaminetriacetic acid and glycol ether. Diaminetetraacetic acid, hexamethylenediaminetetraacetic acid, ethylenediaminediaminediamine (o-hydroxyphenyl) acetic acid, hydroxyethyliminodiacetic acid, iminodiacetic acid, 1,3-diaminopropanetetraacetic acid, 1,2-diaminopropanetetraacetic acid, nitrilotri Acetic acid, nitrilotripropionic acid, triethylenetetraminehexacetic acid, ethylenediaminediaminediponic acid, 1,3-diaminopropanediaminedic acid, glutamate-N, N-diacetic acid, aspartic acid-N, N-diacetate, methylglycinedi Examples thereof include water-soluble aminocarboxylic acid chelate forming agents such as acetic acid, 3-hydroxy-2,2'-iminodi succinic acid, and hydroxycarboxylic acid chelating agents such as gluconic acid, citric acid, tartaric acid, and malic acid. , These can be used by mixing two or more kinds, and these monomers, oligomers and polymers can also be used.

Among these, one or two selected from the group consisting of aminocarboxylic acid chelating agents that do not decompose at high temperatures up to about 200 ° C, especially nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, and triethylenetetraminehexacetic acid. The above is suitable.

Since these aminocarboxylic acid chelating agents have a larger number of ligands than, for example, organic acids, various metal ions can be stabilized in an aqueous solution regardless of fluctuations in pH and the like. It is very useful in the production method of the present invention.

In practice, it is preferable to appropriately select an appropriate one for each metal to be used in consideration of the chelate formation constant with the metal, the stability and solubility of the chelate complex, and the like.

The metal compound used for preparing the metal ion solution containing the chelate complex is not particularly limited as long as it can form a chelate complex by reacting with the chelate agent in an aqueous solvent.

As the metal compound, for example, in addition to metal oxides and hydroxides, salts such as carbonates can be used. Particularly preferred are carbonates, hydroxides, and oxides in which extra ions and the like do not remain after the reaction.

However, since contamination with impure metal components becomes a problem, sodium and potassium, in particular, remain in the electrolyte layer even after firing and cause a disturbance in the composition, so they should be used except when they are actively incorporated into the electrolyte layer. It should be avoided as much as possible.

If the electrolyte layer should contain non-metal elements such as chlorine, phosphorus, sulfur, boron, and silicon, chloride, sulfate, phosphate, borate, silicate, etc. should be used in combination. May be good.

In addition, inorganic acids including chlorine, sulfur, phosphorus, etc .; inorganic acid salts such as hydrochlorides, sulfates, phosphates; organic substances such as thiol compounds also positively contain non-metal components such as chlorine as the composition of the electrolyte layer. It should not be used for similar reasons except when it is contained.

The above non-metal component may be added in an appropriate amount as long as it is decomposed by thermal decomposition or firing, but if it is added in a large amount, it may be contaminated by impurities mixed in, so it should be kept to the minimum necessary. Is.

When a metal having poor reactivity as a metal such as Cr, or a metal having no form of carbonate, nitrate or hydroxide such as Ti and having a poor oxide of oxide is used. First, it is desirable to produce an organic metal chelate aqueous solution using chloride or sulfate, and then prepare high-purity organic metal chelate crystals in advance by crystallization or the like, and use this as a raw material.

In addition to the above-mentioned metals such as Cr and Ti, it is of course possible to prepare high-purity chelate complex crystals obtained by the same method in advance and use them as raw materials.

The composition ratio of the metal components constituting the chelate complex may be the same as the metal composition ratio of the electrolyte layer.

The chelating agent is used in sufficient amount to dissolve all the metal compounds.
Specifically, it is usually preferable to use 1.0 to 1.5 times the molar amount of the total amount of the metal compound.

The aqueous solution of the chelate complex may be prepared by a conventional method.
For example, the chelating agent may be first dissolved in water, then a metal compound may be added and reacted to dissolve the chelating agent.

When two or more kinds of metal oxides are used for the electrolyte layer, the corresponding two or more kinds of metal compounds are added. Alternatively, a solid organometallic chelate may be prepared in advance and dissolved in water.

When the electrolyte layer contains two or more kinds of metal oxides, an aqueous solution of a chelate complex or a chelate complex containing the corresponding two or more kinds of metal ions may be prepared and mixed.

If the chelating agent or chelate complex is not dissolved, ammonia, an organic amine, or the like may be added or heated. The metal compounds may be added sequentially.

Water should be used sufficiently to dissolve the chelating agent and the metal compound, but if it is too much, it takes time to remove it. Therefore, the concentration of the solid content of the chelating agent and the metal compound is usually about 1 to 60% by mass. It should be. The heating temperature is not particularly limited, but usually, the heating / reflux conditions are set from 50 ° C.

In the metal ion solution, the total concentration of metal ions is preferably 3% by mass or more and 25% by mass or less, and more preferably 4% by mass or more and 15% by mass or less.

When the content of the metal ion in the metal ion solution, that is, the metal forming the composite oxide is less than 3% by mass, the metal component contained in the metal ion solution is small, and the electrolyte film may become thin and defects may occur.
On the other hand, if it exceeds 25% by mass, the viscosity of the metal ion solution becomes high, and it may be difficult for the metal ion solution to flow down in the porous anode layer.

The viscosity of the metal ion solution depends on the porous anode layer used, but is preferably 2 to 10 mPa · s (25 ° C.).

If the viscosity of the metal ion solution is less than 2 mPa · s, the metal ion solution gets too wet and spreads on the smoothing member, and the electrolyte membrane becomes thin. If it exceeds 10 mPa · s, it tends to stay in the middle of the porous anode layer.

The viscosity of the metal ion solution can be measured by using a rotary viscometer VISCOMETER TVB-15M manufactured by Toki Sangyo Co., Ltd. using a TM1 rotor at a rotation speed of 60 rpm and setting the temperature of the metal ion solution to 25 ° C.

When the electrolyte membrane is thin and defects occur, a smooth and thin electrolyte membrane without defects can be formed by repeating the production method of the present invention a plurality of times.

Further, in the case of preventing defects in the electrolyte membrane or forming a thick electrolyte membrane on the outside of the porous anode layer, on one side of the porous anode layer, that is, on the surface of the formed electrolyte layer. Further, by laminating the electrolyte layer by the PVD method, the CVD method, or the like, a thick electrolyte membrane can be formed on the outside of the porous anode layer.
Further, by providing a spacer between the smoothing member and the porous anode layer, a thick electrolyte membrane can be formed on the outside of the porous anode layer.

Further, as shown in FIG. 2, it is preferable to apply the thickener 4 to the surface of the smoothing member 2.
By arranging the porous anode layer 1 on the smoothing member 2 having the coating film of the thickener 4 and allowing the metal ion solution 3 to flow down, the range in which the metal ion solution 3 spreads is on the coating film of the thickener 4. It is possible to form a smooth and thin electrolyte membrane without defects.

The thickener may be swelled or dissolved in a metal ion solution to absorb the metal ion solution. For example, polyvinyl alcohol, polyvinylpyrrolidone, hydroethyl cellulose, carboxymethyl cellulos, phenol resin, polyacrylic acid, polyacrylic acid. Water-soluble acrylic resins such as esters, polyacrylic acid ester copolymers, and polymethacrylic acid, and water-soluble resins such as gelatin, starch, and casein can be used.

In addition, the metal ion solution can contain a nonionic surfactant.
When the metal ion solution contains a nonionic surfactant, the surface tension of the metal ion solution is made uniform, the wettability to the porous anode layer is improved, and it becomes easy to flow down in the porous anode layer.
Even if the metal ion solution does not flow down and stays in the middle of the porous anode layer, the nonionic surfactant remains in the system even after thermal decomposition of metal ions, chlorine, phosphorus, sulfur, boron, silicon, etc. Since it does not contain easily non-metal elements, it does not affect the reactivity of the porous anode layer.

Examples of the nonionic surfactant include ester types such as glycerin fatty acid ester and sorbitan fatty acid ester, ether types such as polyoxyalkylene alkyl ether and alkylphenol ethoxylate, and 2,4,7,9-tetramethyl-. Ethylene oxides such as 5-decine-4,7, -diols, 3,6-dimethyl-4-octin-3,6-diols and / or acetylene glycol types such as propylene oxide adducts, 3,5-dimethyl-1. -Ethylene oxide such as hexane-3-ol and / or acetylene alcohol type such as propylene oxide adduct, alkanolamide type, and the like can be used.

The surface tension of the metal ion solution is preferably 80 mN / m or less, although it depends on the pore diameter of the porous anode layer and the like. When the surface tension is 80 mN / m (20 ° C.) or less, it is possible to prevent the metal ion solution from staying in the middle of the porous anode layer. Further, when the surface tension is 40 mN / m (20 ° C.) or less, it becomes easier to penetrate into the fine pores of the porous anode layer.

The surface tension can be measured by the Wilhelmy method at a liquid temperature of 20 ° C. using "CBVP-A3" manufactured by Kyowa Interface Science.

As the porous anode layer, a material conventionally used for a solid oxide fuel cell can be used as a fuel electrode material.

The fuel electrode material is a metal selected from the group consisting of metals such as nickel (Ni), yttrium (Y), zirconium (Zr), palladium (Pd), ruthenium (Ru), and titanium (Ti). The sintered body of the composite oxide particles of the above can be used, and among them, the sintered body of the composite oxide particles represented by the following formula can be preferably used.
(Y ₂ O ₃ ) _1-x (ZrO ₂ ) _x ... Formula However, the range of x in the above formula is 0.03 <x <0.15.

As shown in FIGS. 1 and 2, the porous anode layer 1 preferably includes the porous metal layer 5 on the other surface side.
By being supported by the porous metal layer from the other surface side, the strength is secured by the porous metal layer, and the film thickness can be reduced even in the porous anode layer having a large pore diameter and excellent gas diffusivity. can.

The film thickness of the porous anode layer is preferably 10 μm or more and 100 μm or less, and the average opening diameter of the porous anode layer is preferably 1 μm or more and 5 μm or less.
The porous anode layer in the above range enables rapid start-up and can form a lightweight and miniaturized fuel cell.

The average opening diameter of the porous anode layer can be measured by binarizing the porous anode layer and the surface image by image analysis.

As the porous metal layer, a sintered body of stainless steel particles, a punching metal, or the like can be used.

A method for producing a porous anode layer supported by the porous metal layer will be described.
The method for producing the porous anode layer includes a slurry preparation step, a coating step, a laminating step, and a sintering step.

The slurry for the porous anode layer is formed by mixing ceramic particles and metal particles as main components, and a slurry raw material containing a solvent and a binder.
Further, the slurry for a porous metal layer is formed by mixing a slurry raw material containing a metal powder as a main component and a solvent and a binder.

Examples of the solvent used for the slurry include water and / or an alcohol-based solvent such as methanol, ethanol, 1-propanol (NPA), 2-propanol, ethylene glycol and propylene glycol, and N-methyl-2pyrrolidone (NMP). Examples include organic solvents. As these solvents, only one kind may be used, or two or more kinds may be mixed and used.

The amount of the solvent used is preferably adjusted so that the viscosity of the slurry is suitable for molding when the slurry is molded into a sheet.

As the binder to be added to the slurry, a known organic binder can be appropriately selected and used.

Examples of the organic binder include ethylene-based copolymers, styrene-based copolymers, acrylate-based copolymers, methacrylate-based copolymers, vinyl butyral-based resins, vinyl acetal-based resins, vinylformal-based resins, and vinyl alcohol-based binders. Examples thereof include celluloses such as resins and ethyl cellulose.
If necessary, a plasticizer, a dispersant, or the like may be added to each slurry.

A known stirring device can be appropriately selected and used for mixing the slurry raw materials.

Next, in the coating step, each slurry prepared in the above slurry preparation step is molded into a sheet shape by using a sheet forming method such as a tape casting method using a coating device such as a knife coat or a doctor blade.

A sheet for a porous anode layer and a sheet for a porous metal layer can be obtained by heat-treating the obtained sheets of each slurry after drying, if necessary.

Next, in the laminating step, the porous anode layer sheet and the porous metal layer sheet are laminated in order and laminated to form a laminated body.

Finally, in the sintering step, the laminate can be degreased and sintered to obtain a half cell which is a precursor of the metal support cell. The firing conditions are not particularly limited and can be set to known conditions.
Although the case where the anode layer has a one-layer structure has been described, it is possible to have a multi-layer structure having two or more layers, and the type of slurry to be prepared can be changed according to the number of layers.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to the following Examples.

<Preparation of organometallic chelate aqueous solution>
25% aqueous ammonia (61.3 g) was added to a beaker containing ethylenediaminetetraacetic acid (263.3 g) and water (800 g).

This solution is heated to 60 ° C., and while stirring, cerium carbonate octahydrate (218.3 g) and gadolinium oxide (32.7 g) are slowly added in sequence so as not to spill over, and the mixture is stirred at 100 ° C. for 3 hours. Completely dissolved. Then, it was allowed to cool naturally to room temperature, and water was added to make a total amount of 1000 g to obtain a colorless and transparent organometallic chelate aqueous solution having a metal molar ratio of Ce: Gd = 0.8: 0.2.
The pH of this organometallic chelate aqueous solution was 6.0.

[Example 1]
Water is added to the above organic metal chelate aqueous solution to make an organic metal chelate aqueous solution having a metal ion (Ce ⁴⁺ , Gd ³⁺ ) concentration of 4.8% by mass, and a nonionic surfactant (polyoxyallene alkyl ether: Neugen). XL-80: manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was added in an amount of 0.1% by mass to prepare a metal ion solution.

This metal ion solution had a viscosity of 3.2 mPa · s (25 ° C.) and a surface tension of 27.0 mN / m.

₁ is a porous anode layer having a film thickness of 50 μm and a diameter of 30 mm, which is composed of composite oxide particles ((Y 203) _{0.08 (} ZrO ₂ ) _0.92 ) and is supported by a porous metal layer. It was cut into quarters and placed on a smooth silicon wafer substrate with an oxide film formed on the surface so that the porous anode layer was on the bottom.

About 0.8 ml of the above metal ion solution was dropped from the porous metal layer side to penetrate the porous anode layer and wet the surface of the silicon wafer substrate.

The porous anode layer was placed in a muffle furnace while being placed on the silicon wafer substrate while being kept horizontal, heated to 400 ° C. at a heating rate of 5 ° C./min in an air atmosphere, and the entire SiO ₂ substrate was fired for 1 hour. The electrolyte was naturally cooled to room temperature to obtain an electrolyte for a solid oxide fuel cell.

The surface of the porous anode layer and the surface of the electrolyte layer were observed using a field emission scanning electron microscope FE-SEM (JSM-6700F manufactured by JEOL).
The surface SEM image of the porous anode layer is shown in FIG. 3, and the surface SEM image of the electrolyte for a solid oxide fuel cell of Example 1 is shown in FIG. The average pore size of the porous anode layer was 2.5 μm.

Further, a metal ion solution was dropped onto a SiO ₂ substrate and calcined under the same conditions as in Example 1 to form a composite oxide, and the crystallinity of the composite oxide was measured under the following conditions.
The measurement results are shown in FIG.
X-ray diffractometer: Sample horizontal multipurpose X-ray diffractometer (manufactured by UltimaIV Rigaku)
Voltage: 40 kV
Current: 40 mA
Angle: 10-80 °

From FIG. 5, it can be seen that the electrolyte obtained by firing the metal ion solution has crystallinity.

[Example 2]
Water is added to the above organic metal chelate aqueous solution to prepare a metal ion solution having a metal ion (Ce ⁴⁺ , Gd ³⁺ ) concentration of 9.6% by mass, and a nonionic surfactant (polyoxyalkylene alkyl ether: Neugen) is further prepared. XL-80: manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was added in an amount of 0.1% by mass to prepare a metal ion solution.
This metal ion solution had a viscosity of 4.4 mPa · s (25 ° C.) and a surface tension of 27.7 mN / m (20 ° C.).
An electrolyte for a solid oxide fuel cell was obtained in the same manner as in Example 1 except that this metal ion solution was used. The surface SEM image of the electrolyte for a solid oxide fuel cell of Example 2 is shown in FIG.

[Example 3]
The above organic metal chelate aqueous solution: a nonionic surfactant (polyoxyalkylene alkyl ether: Neugen XL-80: manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) is 0 to a concentration of metal ions (Ce ⁴⁺ , Gd ³⁺ ) of 12.8% by mass. A metal ion solution was prepared by adding the amount to 1% by mass.
This metal ion solution had a viscosity of 5.5 mPa · s (25 ° C.) and a surface tension of 28.0 mN / m (20 ° C.).
An electrolyte for a solid oxide fuel cell was obtained in the same manner as in Example 1 except that this metal ion solution was used. The surface SEM image of the electrolyte for a solid oxide fuel cell of Example 3 is shown in FIG.

[Example 4]
Nonionic surfactant (polyoxyalkylene alkyl ether: Neugen-XL80: manufactured by Dai-ichi Kogyo Seiyaku), nonionic surfactant (2,4,7,9-tetramethyl-5-decyne-4,7) , -The same as in Example 1 except that the ethylene oxide adduct of diol (Ethoxydated-2, 4,7,9-Tetramethyl-5-decyne-4,7-diol): acetylenol E40: manufactured by Kawaken Fine Chemicals Co., Ltd.) is replaced. To prepare a metal ion solution.
This metal ion solution had a viscosity of 3.4 mPa · s (25 ° C.) and a surface tension of 31.3 mN / m (20 ° C.).
An electrolyte for a solid oxide fuel cell was obtained in the same manner as in Example 1 except that this metal ion solution was used. The surface SEM image of the electrolyte for a solid oxide fuel cell of Example 4 is shown in FIG.

[Example 5]
A metal ion solution was prepared in the same manner as in Example 1 except that a nonionic surfactant was not added.
This metal ion solution had a viscosity of 3.3 mPa · s (25 ° C.) and a surface tension of 72.6 mN / m (20 ° C.).
An electrolyte for a solid oxide fuel cell was obtained in the same manner as in Example 1 except that this metal ion solution was used. The surface SEM image of the electrolyte for a solid oxide fuel cell of Example 5 is shown in FIG.

[Example 6]
Distilled water was added to a thickener (polyvinyl alcohol: PVA217: manufactured by KURARAY) to prepare an approximately 15% by mass PVA aqueous solution.
The prepared PVA aqueous solution was dropped on the edge of a smooth silicon wafer substrate having an oxide film formed on the surface, and the PVA aqueous solution was applied onto the silicon wafer substrate by the blade coating method.

An electrolyte for a solid oxide fuel cell was obtained in the same manner as in Example 1 except that the SiO ₂ substrate was used. The surface SEM image of the electrolyte for a solid oxide fuel cell of Example 6 is shown in FIG.
Further, FIG. 11 shows a cross-sectional EM image of the porous anode layer before the electrolyte formation, and FIG. 12 shows a cross-sectional SEM image of the porous anode layer after the electrolyte formation.

From FIG. 12, the surface of the porous anode layer is covered with a very thin electrolyte membrane of 1.0 μm or less formed on the outside of the porous anode layer, and the film thickness is 3.5 μm inside the porous anode layer. It can be seen that the electrolyte layer of is formed.

[Comparative Example 1]
A cerium-gadolium composite oxide film was formed on the porous anode layer supported by the porous metal layer by a CVD method under the condition of aiming at a film thickness of 2 μm to obtain an electrolyte for a solid oxide fuel cell.
FIG. 13 shows a surface SEM image of the electrolyte for a solid oxide fuel cell of Comparative Example 1.

<Evaluation>
The electrolytes for solid oxide fuel cells of Examples 1 to 6 and Comparative Example 1 were evaluated.
The evaluation results are shown in Table 1.

(Gas barrier)
The outer circumference of the solid oxide fuel cell electrolyte was fixed to the pipe using a jig, and the inside of the pipe was evacuated to check for gas leaks.
〇: No gas leak ×: With gas leak

(Insulation)
The electrolyte for a solid oxide fuel cell was sandwiched between a pair of conductive plates, and the electrical insulation between the conductive plates was confirmed.
〇: With insulation ×: No insulation

From the above results, according to the method for producing an electrolyte for a solid oxide fuel cell of the present invention, the pores on one side of the porous anode layer are closed with a metal ion solution, and the surface of the porous anode layer is made of metal. It can be wetted with an ionic solution.
Then, by firing this, even if the surface is a coarse porous anode layer having a surface roughness Rz of 4 μm or more, the pores are completely closed to have a gas blocking property, and the porous anode layer has a gas barrier property. It was confirmed that an electrolyte film having a thickness smaller than the opening diameter of the porous anode layer was formed on the outside to obtain insulating properties.

1 Porous anode layer 11 Pore 12 Contact part 2 Smoothing member 3 Metal ion solution 4 Thickener 5 Porous metal layer

Claims (19)

The filling process of filling the pores of the porous anode layer with a metal ion solution,
A heating step of heating the porous anode layer filled with the metal ion solution to form a solid electrolyte is provided.
The solid oxide is characterized in that the filling step is a process of closing the pores opened on one surface side of the porous anode layer with the metal ion solution and forming a smooth surface with the metal ion solution. A method for manufacturing electrolytes for solid fuel cells. The filling step is characterized in that the porous anode layer is arranged on a horizontal smoothing member, and the metal ion solution is allowed to flow down from the other surface side of the porous anode layer to one surface side. The method for producing an electrolyte for a solid oxide fuel cell according to claim 1. The method for producing an electrolyte for a solid oxide fuel cell according to claim 2, wherein the smoothing member includes a coating film containing a thickener on its surface. The electrolyte for a solid oxide fuel cell according to any one of claims 1 to 3, further comprising a drying step of drying the metal ion solution filled in the pores before the heating step. Manufacturing method. The electrolyte for a solid oxide fuel cell according to any one of claims 1 to 4, wherein a solid electrolyte layer having a thickness of 0.5 μm or more is formed in the porous anode layer. Production method. The solid oxide fuel cell according to any one of claims 1 to 5, further comprising a step of further laminating a solid electrolyte layer on one surface of the porous anode layer after the heating step. A method for manufacturing an electrolyte for a battery. The method for producing an electrolyte for a solid oxide fuel cell according to any one of claims 1 to 6, wherein the metal ion solution is an aqueous solution. The method for producing an electrolyte for a solid oxide fuel cell according to any one of claims 1 to 7, wherein the metal ion solution contains a chelating agent. The solid oxide fuel cell according to claim 8, wherein the chelating agent is at least one selected from the group consisting of nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentacetic acid, and triethylenetetraminehexacetic acid. A method for manufacturing an electrolyte for a battery. The method for producing an electrolyte for a solid oxide fuel cell according to any one of claims 1 to 9, wherein the metal ion solution contains a nonionic surfactant. The electrolyte for a solid oxide fuel cell according to any one of claims 1 to 10, wherein the total concentration of metal ions in the metal ion solution is 3% by mass or more and 25% by mass or less. Production method. The method for producing an electrolyte for a solid oxide fuel cell according to any one of claims 1 to 11, wherein the metal ion solution has a viscosity of 2 to 10 mPa · s (25 ° C.). The method for producing an electrolyte for a solid oxide fuel cell according to any one of claims 1 to 12, wherein the surface tension of the metal ion solution is 80 mN / m (20 ° C.) or less. The solid oxide fuel cell according to any one of claims 1 to 13, wherein the metal ion solution contains ions of at least two or more metals selected from the group consisting of transition metals. How to make electrolytes. The method for producing an electrolyte for a solid oxide fuel cell according to any one of claims 1 to 14, wherein the porous anode layer contains composite oxide particles represented by the following formula.
(Y ₂ O ₃ ) _1-x (ZrO ₂ ) _x ... Formula However, the range of x in the above formula is 0.03 <x <0.15. The method for producing an electrolyte for a solid oxide fuel cell according to any one of claims 1 to 15, wherein the heating temperature in the heating step is 300 ° C. or higher and 700 ° C. or lower. The method for producing an electrolyte for a solid oxide fuel cell according to any one of claims 1 to 16, wherein the porous anode layer includes a porous metal layer on the other surface. The method for producing an electrolyte for a solid oxide fuel cell according to any one of claims 1 to 17, wherein the solid electrolyte has a gas blocking property. The method for producing an electrolyte for a solid oxide fuel cell according to any one of claims 1 to 18, wherein the solid electrolyte has crystallinity.

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