Method for producing coating composition, yttria-stabilized zirconia layer, electrochemical element, electrochemical module, electrochemical device, energy system, solid oxide fuel cell, and solid oxide electrolysis cell

Abstract

The present invention provides a coating composition (b2) with which a film can be formed at low cost by a simple method using a zirconium alkoxide (o) and a yttrium compound (p) as starting materials, and with which a dense yttria-stabilized zirconia layer can be obtained. A coating composition (b2) is obtained that contains a zirconium alkoxide (o), an yttrium compound (p), a chelate compound (q), a polyalkylene glycol (r), a catalyst (s), water (t), and an organic solvent (u).

Description

Method for producing coating composition, yttria-stabilized zirconia layer, electrochemical element, electrochemical module, electrochemical device, energy system, solid oxide fuel cell, and solid oxide electrolysis cell

[0001] The present invention relates to a method for producing a coating composition that can form an yttria-stabilized zirconia layer on the surface of various components by coating, and also to various functional components that are provided with an yttria-stabilized zirconia layer.

[0002] It has been known that yttria-stabilized zirconia (hereinafter sometimes referred to as YSZ) is coated on the surfaces of various components and used in parts that require high hardness and inertness, and in refractory parts used in jet engines, etc. It is also known that it is used as a solid electrolyte in solid oxide fuel cells (SOFCs) that are used at relatively high temperatures. The following technology is an example of an application of YSZ to a solid electrolyte in SOFCs. Patent Document 1 discloses a coating solution in which zirconium alkoxide and yttrium nitrate hydrate are dissolved in a first solvent, which is a common solvent, and then dissolved in a second solvent that homogenizes the solution.

[0003] Here, it is stated that in addition to 1-propanol, 2-propanol and 2-methyl-1-propanol are also suitable as the first solvent, and that benzene, hexane, methanol, ethanol, etc. can also be used (see paragraph 0025). On the other hand, the second solvent is described as a homogenizing solvent, and specifically, it is stated that in addition to 2,4-pentanedione, triethanolamine or diethanolamine can also be used (see paragraph 0024).

[0004] In Non-Patent Document 2, a coating solution was prepared by dissolving titanium alkoxide and barium acetate in 1-propanol as a solvent, and polyvinylpyrrolidone was further added as a stress relaxation agent. The solution was then dip-coated to form a crack-free barium titanate (BaTiO ３) coating film is disclosed. Here, when titanium alkoxide is subjected to a condensation reaction, gel pores (voids) containing unreacted Ti—OH are generated in the titanium alkoxide condensation reaction product. If drying and baking are performed in this state, tensile stress is generated in the coating film, causing defects such as cracks to occur on the coating film surface. Therefore, Non-Patent Document 2 claims that defects such as cracks can be suppressed on the coating film surface by adding polyvinylpyrrolidone to the coating solution, which bonds the amide carbonyl groups of polyvinylpyrrolidone with the unreacted Ti—OH in the gel pores, thereby filling the pores in the titanium alkoxide condensation reaction product (gel).

[0005] Japanese Patent Application Publication No. 7-235317

[0006] Hiromitsu Kozuka, Masahiro Kajimura, Journal of the American Ceramic Society, 83, 1056-1062 (2000)

[0007] However, the technology disclosed in Patent Document 1 has been found to have the following problems: (1) When attempting to form the yttria-stabilized zirconia as an electrolyte layer on the surface of an air electrode formed body made of a porous metal oxide, the formed body is immersed in a coating solution and the dipping operation is repeated to obtain an yttria-stabilized zirconia coating, and therefore, to obtain an yttria-stabilized zirconia film with a thickness of about 1 μm, the dipping operation must be repeated 20 times, which is inferior in terms of productivity.

[0008] (2) When producing a coating solution composition, two steps, dissolution in a first solvent and homogeneous dissolution in a second solvent, are required, making the production process complicated.

[0009] (3) As will be explained later in a comparative example in comparison with the working examples, when this method is adopted, cracks occur all over the coating film, the surface becomes rough and gritty, the coating film peels off easily even with a light touch of a finger, and there are cases where the coating film does not reach the baking stage required after formation.

[0010] Furthermore, it was found that the technology disclosed in Non-Patent Document 2 has the following problems: (1) When polyvinylpyrrolidone is added to a coating composition made from zirconium alkoxide and an yttrium compound as starting materials, the unreacted Zr-OH remaining in the condensation reaction product of the zirconium alkoxide strongly bonds with the amidocarbonyl group of the polyvinylpyrrolidone. This can increase the viscosity of the coating liquid, causing it to gel and clogging the nozzle of the spray gun.

[0011] (2) As will be explained later in a comparative example in comparison with the examples, when this method is used, the surface of the coating film has a rough and granular appearance.

[0012] On the other hand, when a coating film of yttria-stabilized zirconia is generally formed by a sol-gel reaction using zirconium alkoxide and an yttrium compound as starting materials, the hydrolysis rate of zirconium alkoxide is much faster than that of commonly used titanium alkoxides or silicon alkoxides, and therefore, if an attempt is made to make the coating film thicker than 1 μm, defects such as breakage and cracks are likely to occur on the surface.

[0013] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a coating composition that can be used to form a film at low cost by a simple method using zirconium alkoxide and an yttrium compound as starting materials, and that can also provide an yttria-stabilized zirconia layer with few defects such as cracks.

[0014] A first characteristic feature of the present invention is a method for producing a coating composition, which comprises mixing a composition containing a zirconium alkoxide, an yttrium compound, a chelate compound, a polyalkylene glycol, a catalyst, water, and an organic solvent to produce a coating composition.

[0015] The coating composition produced by this method contains water necessary for the hydrolysis of zirconium alkoxide, and further contains a catalyst that induces the hydrolysis and condensation reaction, so that a coating film of a desired thickness can be formed by a simple method of applying the coating composition, for example, using an air spray, etc. The inventors' studies have shown that when the coating composition of the present invention is used, a yttria-stabilized zirconia layer with few defects such as cracks can be easily obtained.

[0016] A second characteristic feature of the present invention is that in the method for producing the coating composition, the content of the zirconium alkoxide in the coating composition is 10 to 30 mass %, the content of the yttrium compound is 1 to 10 mass %, the content of the chelate compound is 3 to 15 mass %, the content of the polyalkylene glycol is 0.3 to 7 wt %, the content of the catalyst is 0.1 to 2 mass %, the content of the water is 0.1 to 2 mass %, and the content of the organic solvent is the remainder.

[0017] If the content of zirconium alkoxide is less than 10% by mass, the raw material tends to be insufficient, and the production of the target product is delayed, whereas if it is more than 30% by mass, hydrolysis and condensation may proceed too quickly.

[0018] If the content of the yttrium compound is less than 1 mass%, the raw material tends to be insufficient, making it difficult to obtain the target product, whereas if it is more than 10 mass%, the amount of yttrium in the produced film may be excessive.

[0019] If the content of the chelate compound is less than 3% by mass, it is difficult to obtain the effect of suppressing the hydrolysis rate and polycondensation rate of the zirconium alkoxide, whereas if it is more than 15% by mass, the hydrolysis rate and polycondensation rate are likely to be excessively suppressed.

[0020] The polyalkylene glycol serves to fill pores (voids) containing unreacted Zr—OH remaining in the condensation reaction product of the zirconium alkoxide. By filling these pores, cracks on the surface of the coating film can be suppressed during drying and baking. Considering its role of filling pores (voids) containing unreacted Zr—OH remaining in the condensation reaction product of the zirconium alkoxide, the amount of polyalkylene glycol added is preferably approximately 0.05 to 0.5 moles per mole of zirconium alkoxide. Furthermore, its content in the coating composition is preferably 0.3 to 7 mass%. If the polyalkylene glycol content is less than 0.3 mass%, it is difficult to achieve the effect of filling pores (voids) containing unreacted Zr—OH remaining in the condensation reaction product of the zirconium alkoxide. On the other hand, if it is more than 7 mass%, hydrolysis and polycondensation of the zirconium alkoxide may be inhibited.

[0021] The catalyst is used as a deflocculating agent to uniformly initiate the dissolution and hydrolysis of the zirconium alkoxide and at the same time uniformly disperse the sol produced by hydrolysis. If the content is less than 0.1% by mass, the catalyst may not be able to fully demonstrate its capabilities. If it is added in excess of 2% by mass, no additional effect will be obtained.

[0022] Water is used to dissolve and hydrolyze the zirconium alkoxide. The amount of water added is preferably about 0.25 to 1.0 mole per mole of zirconium alkoxide. The content of water in the coating composition is preferably 0.1 to 2 mass%.

[0023] Since water is also used for dissolving and hydrolyzing the zirconium alkoxide, if the water content is less than 0.25 mol, the composition will not be able to achieve its purpose of promoting the hydrolysis reaction on its own. Adding more than 1.0 mol will not provide any additional benefits. From the viewpoint of the coatability and ease of handling of the coating composition, a range of about 0.1 to 2 mass % is preferred.

[0024] The organic solvent is used to dissolve the zirconium alkoxide, yttrium compound, chelate compound, polyalkylene glycol, catalyst, and water. The alkoxy group of the zirconium alkoxide is hydrophobic and does not mix with water, so an alcohol that is miscible with both the alkoxide and water is required.

[0025] A third characteristic feature of the present invention is that, in the method for producing a coating composition, the zirconium alkoxide is one or more of zirconium (IV) methoxide, zirconium (IV) ethoxide, zirconium (IV) n-propoxide, zirconium (IV) i-propoxide, zirconium (IV) n-butoxide, zirconium (IV) i-butoxide, zirconium (IV) sec-butoxide, and zirconium (IV) t-butoxide.

[0026] That is, zirconium alkoxides are the starting materials for yttria-stabilized zirconia. Among these, zirconium (IV) n-propoxide, zirconium (IV) i-propoxide, and zirconium (IV) n-butoxide are preferred in terms of availability and hydrolysis property. By combining these compounds with the chelate compound described below, it is possible to obtain an yttria-stabilized zirconia layer that is free from cracking and peeling.

[0027] A fourth characteristic feature of the present invention is that in the method for producing a coating composition, the yttrium compound is one or more of yttrium nitrate, yttrium chloride, yttrium sulfate, yttrium phosphate, yttrium acetate, yttrium carbonate, yttrium (III) ethoxide, yttrium (III) n-propoxide, and yttrium (III) i-propoxide.

[0028] That is, the yttrium compound is a starting material for yttria-stabilized zirconia. When an inorganic acid salt is used as the yttrium compound, it is preferable to use the same type of inorganic acid as the catalyst described below. For example, when yttrium nitrate is used, it is preferable to use nitric acid. The same applies to organic acid salts.

[0029] Among these, yttrium nitrate, yttrium chloride, yttrium sulfate, yttrium phosphate, yttrium carbonate, yttrium acetate, and yttrium (III) i-propoxide are preferred from the viewpoints of availability, reactivity, etc. By using these compounds, it is possible to form an yttria-stabilized zirconia layer by reacting with the hydrolysis product of zirconium alkoxide.

[0030] A fifth characteristic feature of the present invention is that in the method for producing a coating composition, the chelate compound is represented by general formula 1. １ -CO-CH ２ -CO-R ２ (General Formula 1) [In the formula, R1 and R2 are alkyl groups (including fluorinated alkyl groups) having 1 to 6 carbon atoms, or monocyclic or bicyclic aryl groups; R1 and R2 may be the same or different and each is an alkyl group having 1 to 6 carbon atoms, or a monocyclic or bicyclic aryl group. R1 and R2 may be linked to each other to form a cyclic alkyl group.]

[0031] This chelate compound coordinates with the zirconium alkoxide and inhibits the hydrolysis rate and polycondensation rate of the zirconium alkoxide.

[0032] A sixth characteristic feature of the present invention is that, in the method for producing a coating composition, the chelate compound is one or more of 2,4-pentanedione, 2,4-hexanedione, 3,5-heptanedione, 2,6-dimethyl-3,5-heptanedione, 2,2,6,6-tetramethyl-3,5-heptanedione, 1-phenyl-1,3-butanedione, 1,3-diphenyl-1,3-propanedione, 1,1,1-trifluoro-2,4-pentanedione, 1,1,1,5,5,5-hexafluoro-2,4-pentanedione, and 1,3-cyclohexanedione.

[0033] Among these, 2,4-pentanedione, 3,5-heptanedione, 2,6-dimethyl-3,5-heptanedione, 2,2,6,6-tetramethyl-3,5-heptanedione, 1-phenyl-1,3-butanedione, and 1,3-diphenyl-1,3-propanedione are preferred in terms of availability and coordinating power to zirconium alkoxides. １ and R ２ is an electron-donating group such as a methyl group, an ethyl group, a propyl group, a butyl group, or a phenyl group, and therefore has excellent coordination power with zirconium alkoxide, suppressing the hydrolysis reaction rate and polycondensation reaction rate of zirconium alkoxide, thereby making it possible to obtain an yttria-stabilized zirconia layer that is free from cracks and peeling.

[0034] A seventh characteristic feature of the present invention is that in the method for producing a coating composition, the polyalkylene glycol is one or more of tetraethylene glycol, pentaethylene glycol, polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 600, polyethylene glycol 1000, tripropylene glycol, tetrapropylene glycol, polypropylene glycol 400, polypropylene glycol 700, and polypropylene glycol 1000.

[0035] That is, examples of polyalkylene glycols include polyethylene glycol and polypropylene glycol, and the molecular weight of the polyalkylene glycol is preferably about 100 to 2,000, more preferably about 200 to 1,000.

[0036] In the case of polyethylene glycol, it can be represented by the following general formula 2: H(OCH ２ CH ２ ) ｎ OH (General Formula 2) [wherein n is an integer of 2 or more] When n = 4, the molecular weight is 194, and when n = 23, the molecular weight is 1030. Therefore, polyethylene glycols with molecular weights in the range of about 200 to about 1000 are considered to have a molecular size suitable for filling pores (voids) containing unreacted Zr—OH remaining in the condensation reaction product of zirconium alkoxide.

[0037] On the other hand, polypropylene glycol can be represented by the following general formula 3: H(OCHCH ３ CH ２ ) ｎ OH (general formula 3) [wherein n is an integer of 2 or more] When n = 3, the molecular weight is 192, and when n = 17, the molecular weight is 1004. Therefore, polypropylene glycols with molecular weights in the range of about 200 to about 1000 are considered to have a molecular size suitable for filling pores containing unreacted Zr—OH remaining in the condensation reaction product of zirconium alkoxide.

[0038] Among these, tetraethylene glycol, pentaethylene glycol, polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 600, polyethylene glycol 1000, tripropylene glycol, tetrapropylene glycol, polypropylene glycol 400, polypropylene glycol 700, and polypropylene glycol 1000 can be mentioned in terms of availability, molecular size, film-forming properties, and the like.

[0039] An eighth characteristic feature of the present invention is that in the method for producing a coating composition, the catalyst is one or more of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, carbonic acid, and acetic acid.

[0040] Among these, nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and acetic acid are preferred in terms of the hydrolysis and oxidation properties of zirconium alkoxide. By using these acids, zirconium alkoxide can be uniformly hydrolyzed and the resulting sol can be uniformly dispersed in the reaction solution, thereby making it possible to obtain an yttria-stabilized zirconia layer that is free from cracks and peeling.

[0041] A ninth characteristic feature of the present invention is that in the method for producing a coating composition, the organic solvent is one or more of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, and 2-methyl-2-propanol.

[0042] The organic solvent may be used alone or in combination of two or more organic solvents. The organic solvent is the remainder of the other components (zirconium alkoxide, yttrium compound, chelate compound, catalyst, water), and its content in the coating composition is preferably 40 to 80% by mass, while satisfying the requirements of the other components. If the organic solvent content is less than 40% by mass, sufficient mixing performance may not be achieved. If the organic solvent content exceeds 80% by mass, the raw material components tend to be insufficient.

[0043] The alcohol to be used may be, for example, an alcohol corresponding to the alkoxide of the zirconium alkoxide used, but is not particularly limited as long as it can dissolve the zirconium alkoxide and the yttrium compound.

[0044] [Use of Yttria-Stabilized Zirconia Layer] Hereinafter, the case where the yttria-stabilized zirconia layer according to the present invention is used in the "electrochemical element" of the present invention will be described.

[0045] The "electrochemical element" in the present invention is configured by providing a counter electrode layer on the opposite side of an electrode layer with an electrolyte layer sandwiched therebetween.

[0046] When this electrochemical element is operated as a fuel cell, for example, the electrode layer is operated as a fuel electrode layer and the counter electrode layer is operated as an air electrode layer, thereby generating electric power between the two electrodes. That is, by supplying a reducing gas (typically a fuel gas containing hydrogen) to the fuel electrode layer and an oxidizing gas (typically air containing oxygen) to the air electrode layer, the electrochemical element can be operated as a single fuel cell. Conversely, when a predetermined amount of electric power is supplied between the two electrodes, the electrochemical element can be operated as an electrolytic element (electrolysis element) that receives a supply of water and decomposes it. Hereinafter, electrolysis may be simply referred to as electrolysis.

[0047] Therefore, in the present invention, when the electrochemical element is used as a fuel cell, the electrochemical device becomes a fuel cell device, and when the electrochemical element is used as an electrolysis cell, the electrolysis device becomes an electrolysis device.

[0048] The coating composition produced by the coating composition production method according to the present invention can easily produce an yttria-stabilized zirconia layer, and therefore can be employed at least in the production of the electrolyte layer in the present invention. Furthermore, yttria-stabilized zirconia can also be employed as a material for components other than the electrolyte layer used in electrochemical elements, such as a material for an electrode layer or a material for an intermediate layer that may be provided between an electrode layer and an electrolyte layer.

[0049] That is, a tenth characteristic feature of the present invention is that the electrochemical element according to the present invention is provided with an yttria-stabilized zirconia layer obtained by curing the coating composition produced by the method for producing a coating composition according to the present invention.

[0050] An eleventh characteristic feature of the present invention is an electrochemical element including the yttria-stabilized zirconia layer according to the present invention.

[0051] Furthermore, a twelfth characteristic configuration of the present invention is that the electrochemical device has a metal support.

[0052] According to the above characteristic configuration, the electrochemical elements can be supported by a robust metal support, and the required electrical conductivity between the electrochemical elements can be ensured.

[0053] A thirteenth characteristic feature of the present invention is that the present invention is an electrochemical module in which a plurality of the electrochemical elements are arranged in a group.

[0054] According to the above characteristic configuration, a plurality of the above-mentioned electrochemical elements are arranged in a cluster, so that a compact, high-performance electrochemical module with excellent strength and reliability can be obtained while reducing material costs and processing costs.

[0055] A fourteenth characteristic configuration of the present invention is an electrochemical device having the above-mentioned electrochemical element or the above-mentioned electrochemical module, and a fuel converter that supplies a gas containing a reducing gas to the electrochemical element or the electrochemical module, or a fuel converter that converts a gas containing a reducing gas generated in the electrochemical element or the electrochemical module.

[0056] According to the above characteristic configuration, when the electrochemical element or electrochemical module is operated as a fuel cell, hydrogen can be generated from natural gas or the like supplied using an existing raw fuel supply infrastructure such as city gas by a fuel converter such as a reformer, and the hydrogen can be distributed to the fuel cell. Also, when the electrochemical element or electrochemical module is operated as an electrolysis cell, for example, it can be an electrochemical device in which hydrogen generated by the electrolysis reaction of water is reacted with carbon monoxide or carbon dioxide in a fuel converter to convert it into methane or the like.

[0057] A fifteenth characteristic configuration of the present invention is an electrochemical device having at least the above-mentioned electrochemical element or the above-mentioned electrochemical module, and a power converter that extracts power from the electrochemical element or the electrochemical module, or a power converter that supplies power to the electrochemical element or the electrochemical module.

[0058] According to the above characteristic configuration, the power converter can convert the power extracted from the electrochemical element or electrochemical module and provide it for external use, or can supply power from the outside to both, allowing the electrochemical element or electrochemical module to be used for electrolysis. For example, if an inverter is used as the power converter, this is preferable because it can boost the voltage and convert direct current to alternating current, making it easier to utilize the electrical output obtained from the electrochemical module. On the other hand, when used for electrolysis, an electrochemical device can be constructed that obtains direct current from an alternating current power source and performs electrolysis.

[0059] A sixteenth characteristic feature of the present invention is an energy system including the electrochemical device and a waste heat utilization section that reuses heat discharged from the electrochemical device.

[0060] According to the above-mentioned characteristic configuration, since the electrochemical device and the exhaust heat utilization unit that reuses the heat discharged from the electrochemical device are included, it is possible to realize an energy system that is excellent in durability, reliability, performance, and energy efficiency. Furthermore, it is also possible to realize a hybrid system that is excellent in energy efficiency by combining the electrochemical device with a power generation system that generates power by utilizing the combustion heat of unused fuel gas discharged from the electrochemical device.

[0061] A seventeenth characteristic feature of the present invention is a solid oxide fuel cell comprising the electrochemical element described above, in which a power generation reaction occurs in the electrochemical element.

[0062] On the other hand, an eighteenth characteristic configuration of the present invention is a solid oxide electrolysis cell comprising the above electrochemical element, in which an electrolytic reaction occurs.

[0063] Figure showing the manufacturing state of a coating composition Figure showing the manufacturing state of a coating composition containing yttria-stabilized zirconia microparticles Figure showing the coating state of a coating composition Figure showing a microscopic observation photograph of a product dried at 80°C in Example 1 Figure showing a microscopic observation photograph of a product fired at 1000°C in Example 1 X-ray diffraction chart of a product fired at 1000°C in Example 1 Figure showing a microscopic observation photograph of a product dried at 80°C in Example 2 Figure showing a microscopic observation photograph of a product fired at 1000°C in Example 2 X-ray diffraction chart of a product fired at 1000°C in Example 2 Microscopic observation photograph of a product dried at 80°C in Example 3 Microscope observation photograph of the 1000°C fired product of Example 3. X-ray diffraction chart of the 1000°C fired product of Example 3. Microscope observation photograph of the 80°C dried product of Example 4. Microscope observation photograph of the 1000°C fired product of Example 4. Microscope observation photograph of the 80°C dried product of Example 5. Microscope observation photograph of the 1000°C fired product of Example 5. Microscope observation photograph of the 80°C dried product of Example 6. Microscope observation photograph of the 1000°C fired product of Example 6. Microscope observation photograph of the 80°C dried product of Example 7. Microscope observation photograph of the 1000°C fired product of Example 7. Microscope observation photograph of the 80°C dried product of Example 8. Microscope observation photograph of the 1000°C fired product of Example 8. Microscope observation photograph of the 80°C dried product of Example 9. Microscope observation photograph of the 1000°C fired product of Example 9. Microscope observation photograph of the 80°C fired product of Example 10. Microscope observation photograph of the 1000°C fired product of Example 10. Microscope observation photograph of the 80°C dried product of Comparative Example 1. Comparison FIG. 1 is a microscopic photograph of a product fired at 1000°C in Example 1. FIG. 2 is a microscopic photograph of a product dried at 80°C in Comparative Example 3. FIG. 3 is a microscopic photograph of a product fired at 1000°C in Comparative Example 3. FIG. 4 is a cross-sectional view of a main part showing an example of the configuration of an electrochemical element. FIG. 5 is a cross-sectional view of a main part showing an example of the configuration of an electrochemical module. FIG. 6 is a cross-sectional view of a main part showing another example of the configuration of an electrochemical element. FIG. 7 is a view showing another embodiment in which an electrochemical element is used in an electrolysis reaction section. FIG. 8 is a view showing another embodiment equipped with an electrolysis reaction section, a reverse water gas shift reaction section, and a hydrocarbon synthesis reaction section.

[0064] The present invention will be described in detail below based on examples, but the present invention is not limited to these. Figures 1 and 2 show the manufacturing process of coating composition b2 according to the present invention, and Figure 3 shows an example of its application process. Figure 1 shows an example in which coating composition b2 does not contain yttria-stabilized zirconia fine particles Pa, while Figure 2 shows an example in which yttria-stabilized zirconia fine particles Pa are included.

[0065] As explained above, the coating composition b2 produced by the coating composition production method according to the present invention contains a mixture of zirconium alkoxide o, yttrium compound p, chelate compound q, polyalkylene glycol r, catalyst s, water t, and organic solvent u. As shown in Figure 3, this coating composition b2 is applied to a predetermined position, and then dried and baked to harden, thereby forming an yttria-stabilized zirconia (YSZ) layer.

[0066] Here, zirconium alkoxide o is the starting material for the yttria-stabilized zirconia coating layer, and examples thereof include zirconium(IV) methoxide, zirconium(IV) ethoxide, zirconium(IV) n-propoxide, zirconium(IV) i-propoxide, zirconium(IV) n-butoxide, zirconium(IV) i-butoxide, zirconium(IV) sec-butoxide, and zirconium(IV) t-butoxide. The content of this zirconium alkoxide o in composition b2 is preferably 10 to 30 mass%. The following examples and comparative examples show examples using zirconium(IV) n-butoxide.

[0067] Examples of the yttrium compound p include yttrium nitrate, yttrium chloride, yttrium acetate, yttrium carbonate, yttrium(III) ethoxide, yttrium(III) n-propoxide, and yttrium(III) i-propoxide. The content of the yttrium compound p in the coating composition b2 is preferably 1 to 10 mass%. The following examples and comparative examples show examples in which yttrium nitrate is used.

[0068] Examples of chelate compound q include 2,4-pentanedione, 2,4-hexanedione, 3,5-heptanedione, 2,6-dimethyl-3,5-heptanedione, 2,2,6,6-tetramethyl-3,5-heptanedione, 1-phenyl-1,3-butanedione, 1,3-diphenyl-1,3-propanedione, 1,1,1-trifluoro-2,4-pentanedione, 1,1,1,5,5,5-hexafluoro-2,4-pentanedione, and 1,3-cyclohexanedione. The amount of chelate compound q added is preferably approximately 0.5 to 3 moles per mole of zirconium alkoxide. Furthermore, the content of chelate compound q in coating composition b2 is preferably 3 to 15 mass%. The following examples and comparative examples demonstrate the use of 2,4-pentanedione.

[0069] Examples of polyalkylene glycol r include tetraethylene glycol, pentaethylene glycol, polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 600, polyethylene glycol 1000, tripropylene glycol, tetrapropylene glycol, polypropylene glycol 400, polypropylene glycol 700, and polypropylene glycol 1000. Considering its role in filling pores containing unreacted Zr—OH remaining in the condensation reaction product of zirconium alkoxide, the amount of polyalkylene glycol r added is preferably approximately 0.05 to 0.5 moles per mole of zirconium alkoxide. Furthermore, its content in coating composition b2 is preferably 0.3 to 7 mass%. In the examples below, examples using polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 600, tripropylene glycol, polypropylene glycol 400, and polypropylene glycol 700 are shown. When using a polyalkylene glycol having a molecular weight of 700 or less as in these examples, the content in the coating composition is preferably 0.3 to 5% by mass.

[0070] Examples of catalyst s that can be used include hydrochloric acid, acetic acid, nitric acid, sulfuric acid, and phosphoric acid. The content of catalyst s in coating composition b2 is preferably 0.1 to 2 mass %. Examples and comparative examples described below use nitric acid.

[0071] Since water t is also used for the hydrolysis of zirconium alkoxide o, if the amount is less than 0.25 mol, the composition will not be able to independently promote the hydrolysis reaction, and even if more than 1.0 mol is added, no additional effect will be obtained. From the viewpoint of the coatability and ease of handling of coating composition b2, the content of water t in coating composition b2 is preferably in the range of about 0.1 to 2 mass%.

[0072] Examples of organic solvent u include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, and 2-methyl-2-propanol. Organic solvent u represents the remaining amount of other components. In Examples 1 to 10 and Comparative Examples 1 and 3 described below, examples are shown in which a mixed solvent of ethanol and 1-butanol is used. However, since Comparative Example 2 is a reproduction experiment of Patent Document 1, 1-propanol was used in accordance with Patent Document 1.

[0073] Examples 1 to 10 and Comparative Examples 1 to 3 shown below are examples in which a coating composition b2 according to the present invention was applied to the upper surface of test piece B (φ25×3 mm, made of SUS430 stainless steel, with gadolinium-doped ceria b1 screen-printed on the surface), as shown in Fig. 3, and heat-treated at a predetermined temperature for a predetermined time to evaluate whether a target layer, an yttria-stabilized zirconia layer, could be obtained. As will be described later, the yttria-stabilized zirconia layer can be used as the electrolyte layer 4, and the gadolinium-doped ceria b1 is intended as the intermediate layer 3 provided between the electrolyte layer 4 and the electrode layer 2 that constitute the electrochemical element E (see paragraphs

[124] to

[134] and Fig. 30).

[0074] FIG. 1 shows an example of mixing, in which raw materials (zirconium alkoxide o, yttrium compound p, chelate compound q, polyalkylene glycol r, catalyst s, water t, and organic solvent u) are placed in a glass container V1 and mixed using a magnetic stirrer W1 (FIGS. 1(a) and 1(b)). FIG. 2 shows an example of mixing a resin container V2 with yttria-stabilized zirconia fine particles Pa and organic solvent u using a vibration agitator W2 (FIGS. 1(a) and 1(b)). The remaining components (zirconium alkoxide o, yttrium compound p, chelate compound q, polyalkylene glycol r, catalyst s, and water t) are then mixed in the glass container V1 using a magnetic stirrer W1 (FIGS. 1(c) and 1(d)). As shown in FIG. 2, the addition of yttria-stabilized zirconia fine particles Pa as a filler (aggregate) facilitates the desired thickness of the yttria-stabilized zirconia layer (the thickness of the coating film). It is also expected that stress in the yttria-stabilized zirconia layer will be alleviated, preventing defects such as cracks. Figure 3 shows the state in which coating composition b2 is applied to a predetermined surface using air spray X. In the following explanations of the examples and comparative examples, the reference numerals shown in the drawings have been omitted to clarify the names and amounts of each raw material.

[0075] Example 1: 6.40 g of zirconium(IV) n-butoxide, 1.60 g of yttrium nitrate hexahydrate, 3.34 g of 2,4-pentanedione, 0.67 g of polyethylene glycol (average molecular weight 200), 0.26 g of 60% nitric acid, 0.12 g of water, 14.42 g of ethanol, and 21.59 g of 1-butanol were mixed into a 150 ml glass container and stirred for 3 hours using a magnetic stirrer to prepare 50 g of a coating composition. In this Example 1, the amount of polyethylene glycol (average molecular weight 200) added was 0.2 mol per mol of zirconium(IV) n-butoxide. The content in the coating composition was 1.34% by mass. Separately, the coating composition was applied to a test piece as a control using an air spray and then heat-treated at 80°C for 30 minutes to prepare a coating film. The coating film after drying at 80°C was observed under a microscope (optical microscope) at 500x magnification, and the results are shown in Figure 4. As shown in Figure 4, a smooth coating film was obtained, with no defects such as cracks. Furthermore, a coating film was produced by holding the film at 1000°C for 60 minutes. The coating film after firing at 1000°C was observed under a microscope (optical microscope) at 500x magnification, and the results are shown in Figure 5. As shown in Figure 5, the coating film showed no damage such as cracks or peeling, and the film thickness was approximately 2 μm. When the coating film fired at 1000°C was analyzed by X-ray diffraction, clear peaks of yttria-stabilized zirconia were observed at 2θ values ​​of 30, 35, 50, 60, 62, and 74, as shown in Figure 6.

[0076] Example 2: 6.32 g of zirconium(IV) n-butoxide, 1.58 g of yttrium nitrate hexahydrate, 3.30 g of 2,4-pentanedione, 1.32 g of polyethylene glycol (average molecular weight 400), 0.26 g of 60% nitric acid, 0.12 g of water, 14.23 g of ethanol, and 22.88 g of 1-butanol were mixed in a 150 ml glass container and stirred for 3 hours using a magnetic stirrer to prepare 50 g of a coating composition. In this Example 2, the amount of polyethylene glycol (average molecular weight 400) added was 0.2 mol per mol of zirconium(IV) n-butoxide. The content in the coating composition was 2.64% by mass. Separately, the coating composition was applied to a test piece as a control using an air spray and then heat-treated at 80°C for 30 minutes to prepare a coating film. The coating film after drying at 80°C was observed under a microscope (optical microscope) at 500x magnification, and the results are shown in Figure 7. As shown in Figure 7, a smooth coating film was obtained, with no defects such as cracks. Furthermore, a coating film was produced by holding the film at 1000°C for 60 minutes. The coating film after firing at 1000°C was observed under a microscope (optical microscope) at 500x magnification, and the results are shown in Figure 8. As shown in Figure 8, the coating film had no damage such as cracks or peeling, and the film thickness was approximately 2 μm. When the coating film fired at 1000°C was analyzed by X-ray diffraction, clear peaks of yttria-stabilized zirconia were observed at 2θ values ​​of 30, 35, 50, 60, 62, and 74, as shown in Figure 9.

[0077] Example 3: 6.24 g of zirconium(IV) n-butoxide, 1.56 g of yttrium nitrate hexahydrate, 3.26 g of 2,4-pentanedione, 1.95 g of polyethylene glycol (average molecular weight 600), 0.26 g of 60% nitric acid, 0.12 g of water, 14.04 g of ethanol, and 22.59 g of 1-butanol were mixed in a 150 ml glass container and stirred for 3 hours using a magnetic stirrer to prepare 50 g of a coating composition. In this Example 3, the amount of polyethylene glycol (average molecular weight 600) added was 0.2 mol per mol of zirconium(IV) n-butoxide. The content in the coating composition was 3.90% by mass. Separately, the coating composition was applied to a test piece as a control using an air spray and heat-treated at 80°C for 30 minutes to prepare a coating film. The results of microscopic (optical) observation of the coating film after drying at 80°C at 500x magnification are shown in Figure 10. As shown in Figure 10, a smooth coating film was obtained, with no defects such as cracks. Furthermore, a coating film was produced by holding the film at 1000°C for 60 minutes. The results of microscopic (optical) observation of the coating film after firing at 1000°C at 500x magnification are shown in Figure 11. As shown in Figure 11, the coating film showed no damage such as cracks or peeling, and the film thickness was approximately 2 μm. When the coating film fired at 1000°C was analyzed by X-ray diffraction, clear peaks of yttria-stabilized zirconia were observed at 2θ values ​​of 30, 35, 50, 60, 62, and 74, as shown in Figure 12.

[0078] Example 4: 6.47 g of zirconium(IV) n-butoxide, 1.61 g of yttrium nitrate hexahydrate, 3.38 g of 2,4-pentanedione, 0.17 g of polyethylene glycol (average molecular weight 200), 0.27 g of 60% nitric acid, 0.12 g of water, 14.56 g of ethanol, and 23.42 g of 1-butanol were mixed in a 150 ml glass container and stirred for 3 hours using a magnetic stirrer to prepare 50 g of a coating composition. In this Example 4, the amount of polyethylene glycol (average molecular weight 200) added was 0.05 mol per mol of zirconium(IV) n-butoxide. The content in the coating composition was 0.34% by mass. Separately, the coating composition was applied to a test piece as a control using an air spray and then heat-treated at 80°C for 30 minutes to prepare a coating film. The coating film after drying at 80°C was observed under a microscope (optical microscope) at 500x magnification, and the results are shown in Figure 13. As shown in Figure 13, a smooth coating film was formed, with no defects such as cracks. Further, a coating film was produced by holding at 1000°C for 60 minutes. The coating film after baking at 1000°C was observed under a microscope (optical microscope) at 500x magnification, and the results are shown in Figure 14. As shown in Figure 14, the coating film had no damage such as cracks or peeling, and the film thickness was approximately 2 µm.

[0079] Example 5: 6.45 g of zirconium(IV) n-butoxide, 1.61 g of yttrium nitrate hexahydrate, 3.36 g of 2,4-pentanedione, 0.34 g of polyethylene glycol (average molecular weight 200), 0.26 g of 60% nitric acid, 0.12 g of water, 14.51 g of ethanol, and 23.35 g of 1-butanol were mixed into a 150 ml glass container and stirred for 3 hours using a magnetic stirrer to prepare 50 g of a coating composition. In this Example 5, the amount of polyethylene glycol (average molecular weight 200) added was 0.1 mol per 1 mol of zirconium(IV) n-butoxide. The content in the coating composition was 0.67% by mass. Separately, the coating composition was applied to a test piece as a control using an air spray and heat-treated at 80°C for 30 minutes to prepare a coating film. The coating film after drying at 80°C was observed under a microscope (optical microscope) at 500x magnification, and the results are shown in Figure 15. As shown in Figure 15, a smooth coating film was obtained, with no defects such as cracks. Further, a coating film was produced by holding at 1000°C for 60 minutes. The coating film after baking at 1000°C was observed under a microscope (optical microscope) at 500x magnification, and the results are shown in Figure 16. As shown in Figure 16, the coating film had no damage such as cracks or peeling, and the film thickness was approximately 2 μm.

[0080] Example 6: 6.36 g of zirconium(IV) n-butoxide, 1.59 g of yttrium nitrate hexahydrate, 3.32 g of 2,4-pentanedione, 0.99 g of polyethylene glycol (average molecular weight 200), 0.26 g of 60% nitric acid, 0.12 g of water, 14.32 g of ethanol, and 23.04 g of 1-butanol were mixed in a 150 ml glass container and stirred for 3 hours using a magnetic stirrer to prepare 50 g of a coating composition. In this Example 6, the amount of polyethylene glycol (average molecular weight 200) added was 0.3 mol per 1 mol of zirconium(IV) n-butoxide. The content in the coating composition was 1.99% by mass. Separately, the coating composition was applied to a test piece as a control using an air spray and then heat-treated at 80°C for 30 minutes to prepare a coating film. The coating film after drying at 80°C was observed under a microscope (optical microscope) at 500x magnification, and the results are shown in Figure 17. As shown in Figure 17, a smooth coating film was obtained, with no defects such as cracks. Further, a coating film was produced by holding at 1000°C for 60 minutes. The coating film after baking at 1000°C was observed under a microscope (optical microscope) at 500x magnification, and the results are shown in Figure 18. As shown in Figure 18, the coating film had no damage such as cracks or peeling, and the film thickness was approximately 2 μm.

[0081] Example 7: 6.28 g of zirconium(IV) n-butoxide, 1.57 g of yttrium nitrate hexahydrate, 3.28 g of 2,4-pentanedione, 1.64 g of polyethylene glycol (average molecular weight 200), 0.26 g of 60% nitric acid, 0.12 g of water, 14.13 g of ethanol, and 22.73 g of 1-butanol were mixed in a 150 ml glass container and stirred for 3 hours using a magnetic stirrer to prepare 50 g of a coating composition. In this Example 7, the amount of polyethylene glycol (average molecular weight 200) added was 0.5 mol per mol of zirconium(IV) n-butoxide. The content in the coating composition was 3.27% by mass. Separately, the coating composition was applied to a test piece as a control using an air spray and then heat-treated at 80°C for 30 minutes to prepare a coating film. The coating film after drying at 80°C was observed under a microscope (optical microscope) at 500x magnification, and the results are shown in Figure 19. As shown in Figure 19, a smooth coating film was obtained, with no defects such as cracks. Further, a coating film was produced by holding at 1000°C for 60 minutes. The coating film after baking at 1000°C was observed under a microscope (optical microscope) at 500x magnification, and the results are shown in Figure 20. As shown in Figure 20, the coating film had no damage such as cracks or peeling, and the film thickness was approximately 2 µm.

[0082] Example 8: 6.32 g of zirconium(IV) n-butoxide, 1.58 g of yttrium nitrate hexahydrate, 3.30 g of 2,4-pentanedione, 1.32 g of polypropylene glycol (average molecular weight 400), 0.26 g of 60% nitric acid, 0.12 g of water, 14.23 g of ethanol, and 22.88 g of 1-butanol were mixed in a 150 ml glass container and stirred for 3 hours using a magnetic stirrer to prepare 50 g of a coating composition. In this Example 8, the amount of polypropylene glycol (average molecular weight 400) added was 0.2 mol per mol of zirconium(IV) n-butoxide. The content in the coating composition was 2.64% by mass. Separately, the coating composition was applied to a test piece as a control using an air spray and heat-treated at 80°C for 30 minutes to prepare a coating film. The coating film after drying at 80°C was observed under a microscope (optical microscope) at 500x magnification, and the results are shown in Figure 21. As shown in Figure 21, a smooth coating film was obtained, with no defects such as cracks. Further, a coating film was produced by holding at 1000°C for 60 minutes. The coating film after baking at 1000°C was observed under a microscope (optical microscope) at 500x magnification, and the results are shown in Figure 22. As shown in Figure 22, the coating film had no damage such as cracks or peeling, and the film thickness was approximately 2 µm.

[0083] Example 9: 6.41 g of zirconium(IV) n-butoxide, 1.60 g of yttrium nitrate hexahydrate, 3.34 g of 2,4-pentanedione, 0.64 g of tripropylene glycol (molecular weight 192), 0.26 g of 60% nitric acid, 0.12 g of water, 14.42 g of ethanol, and 23.20 g of 1-butanol were mixed in a 150 ml glass container and stirred for 3 hours using a magnetic stirrer to prepare 50 g of a coating composition. In this Example 9, the amount of tripropylene glycol (molecular weight 192) added was 0.2 mol per mol of zirconium(IV) n-butoxide. The content in the coating composition was 1.28% by mass. Separately, the coating composition was applied to a test piece as a control using an air spray and heat-treated at 80°C for 30 minutes to prepare a coating film. The coating film after drying at 80°C was observed under a microscope (optical microscope) at 500x magnification, and the results are shown in Figure 23. As shown in Figure 23, a smooth coating film was obtained, with no defects such as cracks. Further, a coating film was produced by holding at 1000°C for 60 minutes. The coating film after baking at 1000°C was observed under a microscope (optical microscope) at 500x magnification, and the results are shown in Figure 24. As shown in Figure 24, the coating film had no damage such as cracks or peeling, and the film thickness was approximately 2 µm.

[0084] Example 10: 6.20 g of zirconium(IV) n-butoxide, 1.55 g of yttrium nitrate hexahydrate, 3.23 g of 2,4-pentanedione, 2.26 g of polypropylene glycol 700 (average molecular weight 700), 0.25 g of 60% nitric acid, 0.11 g of water, 13.95 g of ethanol, and 22.44 g of 1-butanol were mixed in a 150 ml glass container and stirred for 3 hours using a magnetic stirrer to prepare 50 g of a coating composition. In this Example 10, the amount of polypropylene glycol 700 (average molecular weight 700) added was 0.2 mol per 1 mol of zirconium(IV) n-butoxide. The content in the coating composition was 4.52 mass%. Separately, the coating composition was applied to a test piece as a control using an air spray and heat-treated at 80°C for 30 minutes to prepare a coating film. The coating film after drying at 80°C was observed under a microscope (optical microscope) at 500x magnification, and the results are shown in Figure 25. As shown in Figure 25, a smooth coating film was obtained, with no defects such as cracks. Further, a coating film was produced by holding at 1000°C for 60 minutes. The coating film after baking at 1000°C was observed under a microscope (optical microscope) at 500x magnification, and the results are shown in Figure 26. As shown in Figure 26, the coating film had no damage such as cracks or peeling, and the film thickness was approximately 2 μm.

[0085] Comparative Example 1 This Comparative Example 1 is an example in which polyalkylene glycol was not added. 6.49 g of zirconium (IV) n-butoxide, 1.62 g of yttrium nitrate hexahydrate, 3.39 g of 2,4-pentanedione, 0.27 g of 60% nitric acid, 0.12 g of water, 23.50 g of 1-butanol, and 14.61 g of ethanol were blended into a 150 ml glass container and stirred for 3 hours using a magnetic stirrer to prepare 50 g of a coating composition. Separately, the coating composition was applied to a test piece as a control using an air spray and heat-treated at 80°C for 30 minutes to prepare a coating film. The results of observation of the coating film after drying at 80°C using a microscope (optical microscope) at 500x magnification are shown in Figure 27. As shown in Figure 27, cracks occurred on the surface of the coating film. The coating film was then further maintained at 1000°C for 60 minutes to prepare a coating film. The coating film after firing at 1000° C. was observed under a microscope (optical microscope) at a magnification of 500 times, and the results are shown in Fig. 28. As shown in Fig. 28, cracks were generated throughout the entire coating film, and the film thickness was approximately 2 μm.

[0086] Comparative Example 2 This Comparative Example 2 is an example that reproduces the example of Patent Document 1. Equal amounts of a 0.5 M 1-propanol solution of zirconium (IV) n-propoxide and a 0.087 M 1-propanol solution of yttrium nitrate hexahydrate were mixed in a 150 ml glass container, and then a 0.5 M 1-propanol solution of 2,4-pentanedione was added in an amount such that the zirconium content was 2 (molar ratio) to the 2,4-pentanedione, to prepare 50 g of a coating composition. Separately, the coating composition was applied to a test piece as a control by air spray and heat-treated at 80°C for 30 minutes. The entire coating film developed a rough, granular appearance, and the coating film easily peeled off with just a light touch of a finger. Peeling of the coating film was confirmed visually after drying at 80°C, so microscope observation and baking at 1000°C were not performed.

[0087] In Comparative Example 2, nitric acid and water as catalysts were not added, so hydrolysis of zirconium (IV) n-propoxide was insufficient, and the polycondensation reaction proceeded only partially, resulting in a rough, granular appearance over the entire surface of the coating film, which is thought to have been the reason for the coating film peeling off easily.

[0088] Comparative Example 3: This Comparative Example 3 is an example in which polyvinylpyrrolidone was added with reference to Non-Patent Document 2. 6.49 g of zirconium(IV) n-butoxide, 1.62 g of yttrium nitrate hexahydrate, 3.39 g of 2,4-pentanedione, 0.65 g of polyvinylpyrrolidone (average molecular weight 25,000), 0.27 g of 60% nitric acid, 0.12 g of water, 14.61 g of ethanol, and 22.85 g of 1-butanol were mixed into a 150 ml glass container and stirred for 3 hours using a magnetic stirrer to produce 50 g of coating composition. In this Comparative Example 3, the amount of polyvinylpyrrolidone (average molecular weight 25,000) added was 10% by mass of zirconium(IV) n-butoxide because the average molecular weight was a large value of 25,000. The content in the coating composition was 1.30% by mass. Separately, the coating composition was applied to a test piece as a control by air spraying, followed by heat treatment at 80°C for 30 minutes to produce a coating film. The coating film after drying at 80°C was observed under a microscope (optical microscope) at 500x magnification, and the results are shown in Figure 29. As shown in Figure 29, there were no cracks, but the coating film had some unevenness. A coating film was then produced by holding the film at 1000°C for 60 minutes. Visual inspection of the coating film after baking at 1000°C revealed a rough surface with many irregularities. Figure 30 shows the results of observation under a microscope (optical microscope) at 500x magnification. As shown in Figure 30, the coating film had many convex surfaces, and the film thickness was approximately 2 μm. Because the surface was rough and uneven to the naked eye, X-ray diffraction analysis was not performed.

[0089] Examples of combinations that can be used to obtain a suitable coating composition b2 and an yttria-stabilized zirconia coating film using zirconium alkoxide o, yttrium compound p, chelate compound q, polyalkylene glycol r, catalyst s, water t, and organic solvent u include the combinations described in Examples 1 to 10, as well as the following combinations, although the present invention is not limited to these combinations.(a) Zirconium (IV) n-butoxide, yttrium nitrate, 2,4-pentanedione, tetraethylene glycol, nitric acid, water, ethanol, 1-butanol (b) Zirconium (IV) n-butoxide, yttrium nitrate, 2,4-pentanedione, pentaethylene glycol, nitric acid, water, ethanol, 1-butanol (c) Zirconium (IV) n-butoxide, yttrium nitrate, 2,4-pentanedione, polyethylene glycol (average molecular weight 1000), nitric acid, water, ethanol, 1-butanol (d) Zirconium (IV) n-butoxide, yttrium nitrate, 2,4-pentanedione, tetrapropylene glycol, nitric acid, water, ethanol, 1-butanol (e) Zirconium (IV) n-butoxide, yttrium nitrate, 2,4-pentanedione, polypropylene glycol (average molecular weight 1000), nitric acid, water, ethanol, 1-butanol (f) Zirconium (IV) n-butoxide, yttrium nitrate, 3,5-heptanedione, polyethylene glycol (average molecular weight 200), nitric acid, water, ethanol, 1-butanol (g) Zirconium (IV) n-propoxide, yttrium nitrate, 2,4-pentanedione, polyethylene glycol (average molecular weight 200), nitric acid, water, ethanol, 1-propanol (h) Zirconium (IV) n-propoxide, yttrium nitrate, 2,4-pentanedione, polyethylene glycol (average molecular weight 400), nitric acid, water, ethanol, 1-propanol (i) Zirconium (IV) n-propoxide, yttrium nitrate, 2,4-pentanedione, polyethylene glycol (average molecular weight 600), nitric acid, water, ethanol, 1-propanol (j) Zirconium (IV) n-butoxide, yttrium chloride, 2,4-heptanedione, polyethylene glycol (average molecular weight 200), hydrochloric acid, water, ethanol, 1-butanol (k) Zirconium (IV) n-butoxide, yttrium sulfate, 2,4-heptanedione, polyethylene glycol (average molecular weight 200), sulfuric acid, water, ethanol, 1-butanol (l) Zirconium (IV) n-butoxide, yttrium acetate, 2,4-heptanedione, polyethylene glycol (average molecular weight 200), acetic acid, water, ethanol, 1-butanol.

[0090] [Use of Yttria-Stabilized Zirconia Layer] Hereinafter, with reference to FIGS. 31 to 34 , a solid oxide fuel cell will be described in which the yttria-stabilized zirconia layer described above is used to form an electrochemical element E, and further, the solid oxide fuel cell is configured to include this electrochemical element E.

[0091] The electrochemical element E is used, for example, as a component of a solid oxide fuel cell that generates electricity by receiving a supply of hydrogen-containing fuel gas and air and causing a power generation reaction. Hereinafter, when describing the positional relationship of layers in the explanation related to the electrochemical element E, the electrolyte layer 4 is used as the reference layer for notating the positions, and the side of the counter electrode layer 6 as viewed from the electrolyte layer 4 may be referred to as "top" or "upper side" (upper side in FIG. 31 ), and the side of the electrode layer 2 may be referred to as "bottom" or "lower side." Furthermore, the side of the metal substrate 1 on which the electrode layer 2 is formed (upper side in FIG. 31 ) may be referred to as the "front side," and the opposite side (lower side in FIG. 31 ) may be referred to as the "back side."

[0092] 31 , the electrochemical element E has a metal substrate 1 (an example of a metal support), an electrode layer 2 formed on the metal substrate 1, an intermediate layer 3 formed on the electrode layer 2, and an electrolyte layer 4 formed on the intermediate layer 3. The electrochemical element E further has a reaction prevention layer 5 formed on the electrolyte layer 4, and a counter electrode layer 6 formed on the reaction prevention layer 5. In other words, the counter electrode layer 6 is formed on the electrolyte layer 4, and the reaction prevention layer 5 is formed between the electrolyte layer 4 and the counter electrode layer 6. The electrode layer 2 and the counter electrode layer 6 are porous, and the electrolyte layer 4 is dense.

[0093] As explained above, the main elements of the layers constituting the electrochemical element E are the electrolyte layer 4, the electrode layer 2 sandwiched between it, and the counter electrode layer 6, and the electrochemical element E can be operated by providing these three layers.

[0094] (Metal Substrate) The metal substrate 1 serves as a support that supports the electrode layer 2, intermediate layer 3, electrolyte layer 4, etc., and maintains the strength of the electrochemical element E. A plate-shaped metal substrate 1 is used as this metal substrate, but the metal support may have other shapes, such as a box shape, a cylinder shape, or a disk shape. The metal substrate 1 may be strong enough to serve as a support for forming the electrochemical element E, and may have a thickness of, for example, about 0.1 mm to 2 mm, preferably about 0.1 mm to 1 mm, and more preferably about 0.1 mm to 0.5 mm.

[0095] The metal substrate 1 has a plurality of through-holes 1a extending from the front surface to the back surface. For example, the through-holes 1a can be formed in the metal substrate 1 by mechanical, chemical, or optical drilling. The through-holes 1a function to allow gas to pass from the back surface to the front surface of the metal substrate 1. Porous metal can also be used to impart gas permeability to the metal substrate 1. For example, sintered metal or foam metal can also be used for the metal substrate 1. Ferritic stainless steel (an example of an Fe—Cr alloy) is used as the metal substrate material. Furthermore, as shown in FIG. 31 , a coating layer 1b may be formed on the outer surface of the metal substrate 1 (including the surfaces of the through-holes 1a). This coating layer 1b can be a metal oxide layer. For example, a Fe—Cr alloy can be subjected to a Co coating process followed by an oxidation process to form a metal oxide layer.

[0096] When an Fe—Cr alloy is used as the material for the metal substrate 1, the thermal expansion coefficient of this material becomes close to that of YSZ (yttria-stabilized zirconia) or GDC (gadolinium-doped ceria, also known as CGO), which are used as materials for the electrode layer 2 and the electrolyte layer 4. As a result, the electrochemical element E is less susceptible to damage even when subjected to repeated temperature cycles of low and high temperatures. This is preferable because it allows for the realization of an electrochemical element E with excellent long-term durability.

[0097] (Electrode Layer) As shown in FIG. 31 , the electrode layer 2 can be formed as a thin layer on the front surface of the metal substrate 1 in an area larger than the area where the through holes 1 a are formed. When the electrode layer 2 is formed as a thin layer, its thickness can be, for example, about 1 μm to 100 μm, preferably 5 μm to 50 μm. Such a thickness makes it possible to reduce the amount of expensive electrode layer material used, thereby reducing costs, while ensuring sufficient electrode performance. The entire area where the through holes 1 a are formed is covered by the electrode layer 2. In other words, the through holes 1 a are formed inside the area of ​​the metal substrate 1 where the electrode layer 2 is formed. In other words, all of the through holes 1 a are provided facing the electrode layer 2.

[0098] Examples of materials for the electrode layer 2 include NiO-GDC, Ni-GDC, NiO-YSZ, Ni-YSZ, and CuO-CeO. ２ , Cu—CeO ２ Examples of such composite materials include YSZ, GDC, CeO ２ can be called the aggregate of the composite material. The electrode layer 2 is preferably formed by a low-temperature firing method (e.g., a wet method using firing in a low-temperature range without firing in a high-temperature range above 1100°C), a spray coating method (thermal spraying, aerosol deposition, aerosol gas deposition, powder jet deposition, particle jet deposition, cold spray, etc.), a PVD method (sputtering, pulsed laser deposition, etc.), a CVD method, etc. By using such a process that can be used in a low-temperature range, a good electrode layer 2 can be obtained without firing in a high-temperature range above 1100°C, for example. Therefore, it is preferable because it is possible to realize an electrochemical element E with excellent durability without damaging the metal substrate 1 and suppressing interdiffusion of elements between the metal substrate 1 and the electrode layer 2. Furthermore, using a low-temperature firing method is even more preferable because it facilitates handling of the raw materials.

[0099] The electrode layer 2 has a plurality of pores inside and on its surface to provide gas permeability. That is, the electrode layer 2 is formed as a porous layer. For example, the electrode layer 2 is formed so that its density is 30% or more and less than 80%. The size of the pores can be appropriately selected so that the electrochemical reaction proceeds smoothly. Note that density is the proportion of the space occupied by the material constituting the layer, and can be expressed as (1 - porosity), and is equivalent to the relative density.

[0100] (Intermediate Layer) As shown in FIG. 31 , the intermediate layer 3 can be formed as a thin layer on the electrode layer 2, covering the electrode layer 2. When the intermediate layer 3 is formed as a thin layer, its thickness can be, for example, approximately 1 μm to 100 μm, preferably approximately 2 μm to 50 μm, and more preferably approximately 4 μm to 25 μm. This thickness reduces the amount of expensive intermediate layer material used, thereby reducing costs, while ensuring sufficient performance. Examples of materials that can be used for the intermediate layer 3 include YSZ (yttria-stabilized zirconia), SSZ (scandia-stabilized zirconia), GDC (gadolinium-doped ceria), YDC (yttrium-doped ceria), and SDC (samarium-doped ceria). Ceria-based ceramics are particularly preferred.

[0101] The intermediate layer 3 is preferably formed by a low-temperature firing method (e.g., a wet method using firing in a low-temperature range without firing in a high-temperature range above 1100°C), a spray coating method (such as thermal spraying, aerosol deposition, aerosol gas deposition, powder jet deposition, particle jet deposition, or cold spray), a PVD method (such as sputtering or pulsed laser deposition), or a CVD method. These film-forming processes that can be used in low-temperature ranges allow the intermediate layer 3 to be obtained without firing in a high-temperature range above 1100°C, for example. Therefore, interdiffusion of elements between the metal substrate 1 and the electrode layer 2 can be suppressed without damaging the metal substrate 1, resulting in an electrochemical element E with excellent durability. Furthermore, using a low-temperature firing method is even more preferable because it facilitates handling of raw materials.

[0102] The intermediate layer 3 preferably has oxygen ion (oxide ion) conductivity. It is more preferable that the intermediate layer 3 has mixed conductivity of oxygen ions (oxide ions) and electrons. The intermediate layer 3 having these properties is suitable for application to the electrochemical element E.

[0103] (Electrolyte Layer) As shown in FIG. 31 , the electrolyte layer 4 is formed as a thin layer on the intermediate layer 3, covering the electrode layer 2 and the intermediate layer 3. It can also be formed as a thin film with a thickness of 10 μm or less. Specifically, the electrolyte layer 4 is provided over (straddles) the intermediate layer 3 and the metal substrate 1. By configuring it in this way and bonding the electrolyte layer 4 to the metal substrate 1, the electrochemical element E as a whole can be made to have excellent robustness. Furthermore, the electrolyte layer 4 is provided on the front surface of the metal substrate 1 in an area larger than the area in which the through-hole 1 a is provided. In other words, the through-hole 1 a is formed inside the area in the metal substrate 1 in which the electrolyte layer 4 is formed.

[0104] Furthermore, gas leakage from the electrode layer 2 and intermediate layer 3 can be suppressed around the electrolyte layer 4. That is, when the electrochemical element E is used as a component of an SOFC, gas is supplied to the electrode layer 2 from the back side of the metal substrate 1 through the through holes 1 a during SOFC operation. Gas leakage can be suppressed in the area where the electrolyte layer 4 contacts the metal substrate 1 without providing a separate member such as a gasket. Note that, although the electrolyte layer 4 completely covers the periphery of the electrode layer 2 in this embodiment, a configuration in which the electrolyte layer 4 is provided on top of the electrode layer 2 and intermediate layer 3 and a gasket or the like is provided around the periphery may also be adopted.

[0105] Examples of materials that can be used for the electrolyte layer 4 include YSZ (yttria-stabilized zirconia), SSZ (scandia-stabilized zirconia), GDC (gadolinium-doped ceria), YDC (yttrium-doped ceria), SDC (samarium-doped ceria), and LSGM (strontium-magnesium-doped lanthanum gallate). Zirconia-based ceramics are particularly suitable. Using zirconia-based ceramics for the electrolyte layer 4 allows the operating temperature of an SOFC using the electrochemical element E to be higher than that of ceria-based ceramics. For example, when the electrochemical element E is used in an SOFC, a material such as YSZ that can exhibit high electrolyte performance even at high temperatures of approximately 650°C or higher is used for the electrolyte layer 4. A hydrocarbon-based raw fuel, such as city gas or LPG, is used as the raw fuel for the system, and the raw fuel is converted into the SOFC anode gas by steam reforming or the like. This allows for the construction of a highly efficient SOFC system in which heat generated in the SOFC cell stack is used to reform the raw fuel gas.

[0106] The electrolyte layer 4 is preferably formed by a low-temperature firing method (a wet method using a firing treatment in a low-temperature range that does not involve firing at a high temperature above 1100°C). For example, the electrolyte layer 4 can be formed by applying a liquid composition by air spraying, bar coating, dispenser coating, brushing, or spatula coating, followed by firing at a temperature below 1100°C. Alternatively, the electrolyte layer 4 is preferably formed by a spray coating method (such as thermal spraying, aerosol deposition, aerosol gas deposition, powder jet deposition, particle jet deposition, or cold spray), a PVD method (such as sputtering or pulsed laser deposition), or a CVD method. By using these film-forming processes that can be used in a low-temperature range, an electrolyte layer 4 that is dense and has high airtightness and gas barrier properties can be obtained without firing at a high temperature above 1100°C. Therefore, damage to the metal substrate 1 can be suppressed, and interdiffusion of elements between the metal substrate 1 and the electrode layer 2 can be suppressed, resulting in an electrochemical element E with excellent performance and durability. In particular, using a low-temperature firing method or a spray coating method is preferable because it allows for the realization of a low-cost element. Furthermore, using a low-temperature firing method or a spray coating method is even more preferable because it makes it easy to obtain a dense electrolyte layer 4 that is airtight and has high gas barrier properties at a low temperature.

[0107] The electrolyte layer 4 is densely configured to prevent gas leakage of the anode gas and the cathode gas and to exhibit high ionic conductivity. The density of the electrolyte layer 4 is preferably 90% or more, more preferably 95% or more, and even more preferably 98% or more. When the electrolyte layer 4 is a uniform layer, the density thereof is preferably 95% or more, and more preferably 98% or more. Furthermore, when the electrolyte layer 4 is configured in a multi-layer structure, it is preferable that at least a portion of the layers include a layer having a density of 98% or more (a dense electrolyte layer), and more preferably a layer having a density of 99% or more (a dense electrolyte layer). When such a dense electrolyte layer is included as part of the electrolyte layer 4, it is easier to form an electrolyte layer 4 that is dense and has high airtightness and gas barrier properties, even when the electrolyte layer 4 is configured in a multi-layer structure.

[0108] (Reaction Prevention Layer) The reaction prevention layer 5 can be formed as a thin layer on the electrolyte layer 4. When the reaction prevention layer 5 is formed as a thin layer, its thickness can be, for example, approximately 1 μm to 100 μm, preferably approximately 2 μm to 50 μm, and more preferably approximately 4 μm to 25 μm. This thickness reduces the amount of expensive reaction prevention layer material used, thereby reducing costs, while ensuring sufficient performance. The material for the reaction prevention layer 5 can be any material that can prevent reactions between the components of the electrolyte layer 4 and the components of the counter electrode layer 6. For example, a ceria-based material can be used. By introducing the reaction prevention layer 5 between the electrolyte layer 4 and the counter electrode layer 6, reactions between the constituent materials of the counter electrode layer 6 and the electrolyte layer 4 are effectively suppressed, thereby improving the long-term stability of the performance of the electrochemical element E. Forming the reaction prevention layer 5 using an appropriate method capable of forming the layer at a processing temperature of 1100°C or less is preferable because it can suppress damage to the metal substrate 1 and also suppress interdiffusion of elements between the metal substrate 1 and the electrode layer 2, thereby realizing an electrochemical element E with excellent performance and durability. For example, low-temperature firing (e.g., a wet method using firing at a low temperature range without firing at a high temperature range exceeding 1100°C), spray coating (thermal spraying, aerosol deposition, aerosol gas deposition, powder jet deposition, particle jet deposition, cold spray, etc.), PVD (sputtering, pulsed laser deposition, etc.), CVD, etc. can be appropriately used. In particular, low-temperature firing and spray coating methods are preferable because they allow for low-cost elements to be realized. Furthermore, low-temperature firing is even more preferable because it facilitates handling of raw materials.

[0109] (Counter Electrode Layer) The counter electrode layer 6 can be formed as a thin layer on the electrolyte layer 4 or the reaction prevention layer 5. When the counter electrode layer 6 is formed as a thin layer, its thickness can be, for example, approximately 1 μm to 100 μm, preferably 5 μm to 50 μm. This thickness reduces the amount of expensive counter electrode layer material used, thereby reducing costs, while ensuring sufficient electrode performance. Examples of materials that can be used for the counter electrode layer 6 include composite oxides such as lanthanum strontium cobaltite ferrite (LSCF) and lanthanum strontium manganate (LSM), ceria-based oxides, and mixtures thereof. It is particularly preferred that the counter electrode layer 6 contain a perovskite-type oxide containing two or more elements selected from the group consisting of La, Sr, Sm, Mn, Co, and Fe. The counter electrode layer 6 formed using these materials functions as a cathode.

[0110] The counter electrode layer 6 is preferably formed using a method capable of forming the counter electrode layer 6 at a processing temperature of 1100°C or less, since this suppresses damage to the metal substrate 1 and also suppresses interdiffusion of elements between the metal substrate 1 and the electrode layer 2, thereby realizing an electrochemical element E with excellent performance and durability. For example, low-temperature firing (e.g., a wet method using firing in a low-temperature range without firing in a high-temperature range exceeding 1100°C), spray coating (thermal spraying, aerosol deposition, aerosol gas deposition, powder jet deposition, particle jet deposition, cold spray, etc.), PVD (sputtering, pulsed laser deposition, etc.), CVD, etc., can be appropriately used. In particular, low-temperature firing and spray coating methods are preferred because they allow for the realization of low-cost elements. Furthermore, low-temperature firing is even more preferred because it facilitates handling of raw materials.

[0111] As described above, in the electrochemical element E according to the present invention, a YSZ (yttria-stabilized zirconia) layer can be used for the electrolyte layer 4. Because of the advantages of obtaining a dense electrolyte layer 4 with high airtightness and gas barrier properties, the electrolyte layer 4 can be formed using the coating composition b2 according to the present invention. In another embodiment, an yttria-stabilized zirconia layer obtained by curing the coating composition b2 of the present application can also be used for the electrode layer 2 or part of the intermediate layer 3 (part of a component of the composite material). Furthermore, a separate intermediate layer (not shown) may be inserted between the electrolyte layer 4 and the reaction prevention layer 5, and the yttria-stabilized zirconia layer obtained by curing the coating composition b2 of the present application can also be used for part of this intermediate layer.

[0112] (Operation as a Solid Oxide Fuel Cell) By configuring the electrochemical element E as described above, the electrochemical element E can be used as a fuel cell of a solid oxide fuel cell. For example, a reducing gas (typically a fuel gas containing hydrogen) is supplied to the electrode layer 2 from the rear surface of the metal substrate 1 through the through-holes 1a, and an oxidizing gas (typically air containing oxygen) is supplied to the counter electrode layer 6, which is the counter electrode of the electrode layer 2, and the electrochemical element E is operated at a temperature of, for example, 600°C or higher and 850°C or lower. In this case, the oxygen O contained in the air is oxidized in the counter electrode layer 6. ２ is electron e － reacts with oxygen ions O ２－ The oxygen ions O ２－ The hydrogen H contained in the supplied fuel gas moves through the electrolyte layer 4 to the electrode layer 2 (see FIG. 31). ２ is oxygen ion O ２－ reacts with water H ２ O and electron e － The above reaction generates an electromotive force between the electrode layer 2 and the counter electrode layer 6. In this case, the electrode layer 2 functions as the fuel electrode (anode) of the SOFC, and the counter electrode layer 6 functions as the air electrode (cathode).

[0113] (Manufacturing Method of Electrochemical Element) Next, a manufacturing method of the electrochemical element E according to this embodiment will be described. The following explanation mainly focuses on an example in which a yttria-stabilized zirconia layer is formed on the electrode layer 2, part of the intermediate layer 3, and also on the electrolyte layer 4 using the coating composition b2 according to the present invention.

[0114] (Metal Substrate Preparation Step) In the metal substrate preparation step, a plate made of an Fe—Cr alloy having a predetermined shape is prepared, and a large number of through holes 1 a can be formed in predetermined positions of this plate by laser processing or the like. Alternatively, this plate may be subjected to a Co plating process, and then an oxidation process may be performed after the plating process to form a metal oxide layer containing Co. This metal oxide layer will be formed as a metal oxide layer 1 b (coating layer) in the electrode layer formation step described below.

[0115] (Electrode Layer Formation Step) In the electrode layer formation step, the electrode layer 2 is formed in a thin film state on a region on the front surface of the metal substrate 1 obtained in the metal substrate preparation step that is wider than the region where the through holes 1 a are formed. The through holes 1 a in the metal substrate 1 can be formed by laser processing or the like. As described above, the electrode layer 2 can be formed by a low-temperature firing method (a wet method in which firing is performed at a low temperature of 1100°C or less), a spray coating method (thermal spraying, aerosol deposition, aerosol gas deposition, powder jet deposition, particle jet deposition, cold spray, etc.), a PVD method (sputtering, pulsed laser deposition, etc.), or the like. Whichever method is used, it is preferable to perform the process at a temperature of 1100°C or less to suppress deterioration of the metal substrate 1.

[0116] When the electrode layer formation step is performed using a low-temperature firing method, specifically, a material powder and a solvent (dispersion medium) are mixed to create a material paste, which is then applied to the front surface of the metal substrate 1. Here, the coating composition b2 according to the present invention can be used as a part of this material paste. The electrode layer 2 is then compression-molded (electrode layer smoothing step) and fired at 1100°C or less (electrode layer firing step). Compression molding of the electrode layer 2 can be performed, for example, by CIP (cold isostatic pressing), roll pressing, RIP (rubber isostatic pressing), or the like. Furthermore, firing of the electrode layer 2 is preferably performed at a temperature of 800°C or higher and 1100°C or lower. The order of the electrode layer smoothing step and the electrode layer firing step can also be reversed.

[0117] In the case of forming an electrochemical element E having an intermediate layer 3, the electrode layer smoothing step and the electrode layer firing step may be omitted, or the electrode layer smoothing step and the electrode layer firing step may be included in the intermediate layer smoothing step and the intermediate layer firing step described later. The electrode layer smoothing step may also be performed by performing lapping, leveling, surface cutting, polishing, or the like.

[0118] (Diffusion-Inhibiting Layer Formation Step) The diffusion-inhibiting layer becomes a metal oxide layer 1b (coating layer) formed on the surface of the metal substrate 1 during the firing process in the electrode layer formation step. Incidentally, it is preferable for the firing process to include a firing process in which the firing atmosphere is set under atmospheric conditions with a low oxygen partial pressure, since this effectively inhibits interdiffusion of elements and forms a high-quality metal oxide layer 1b with low resistance. The electrode layer formation step may also include a separate diffusion-inhibiting layer formation step, including when a coating method without firing is used. For example, in the separate diffusion-inhibiting layer formation step, the metal oxide layer 1b is formed by coating Co on the metal substrate 1 and then oxidizing it. Alternatively, for example, in the separate diffusion-inhibiting layer formation step, the metal oxide layer 1b can be formed by coating Co on an intermediate layer formed on the metal substrate 1 and then oxidizing it.

[0119] In either case, it is desirable to carry out the treatment at a temperature of 1100° C. or less, which is capable of suppressing damage to the metal substrate 1. Furthermore, a metal oxide layer 1 b (diffusion suppression layer) may be formed on the surface of the metal substrate 1 during the firing process in the intermediate layer formation step described below.

[0120] (Intermediate Layer Forming Step) In the intermediate layer forming step, the intermediate layer 3 is formed in a thin layer state on the electrode layer 2 so as to cover the electrode layer 2. As described above, the intermediate layer 3 can be formed by a low-temperature firing method (a wet method in which firing is performed in a low temperature range of 1100°C or less), a spray coating method (a thermal spray method, an aerosol deposition method, an aerosol gas deposition method, a powder jet deposition method, a particle jet deposition method, a cold spray method, or the like), a PVD method (a sputtering method, a pulsed laser deposition method, or the like), a CVD method, or the like. Whichever method is used, it is preferable to perform the method at a temperature of 1100°C or less in order to suppress deterioration of the metal substrate 1.

[0121] When the intermediate layer formation step is performed using a low-temperature firing method, the following specific example is performed. First, a material powder for the intermediate layer 3 is mixed with a solvent (dispersion medium) to create a material paste, which is then applied to the front surface of the metal substrate 1. Ceria-based ceramics such as GDC (gadolinium-doped ceria), YDC (yttrium-doped ceria), and SDC (samarium-doped ceria) are preferably used as the material for the intermediate layer 3. If the coating composition b2 according to the present invention is included in this material paste, it can be used as part of the intermediate layer 3 made of a composite material. The intermediate layer 3 is then compression-molded (intermediate layer smoothing step) and fired at 1100°C or less (intermediate layer firing step). The intermediate layer 3 can be rolled, for example, by CIP (cold isostatic pressing), roll pressing, or RIP (rubber isostatic pressing). Furthermore, it is preferable to perform the firing of the intermediate layer 3 at a temperature of 800°C or higher and 1100°C or lower. This is because, at such a temperature, a high-strength intermediate layer 3 can be formed while suppressing damage and deterioration of the metal substrate 1. Furthermore, it is more preferable to perform the firing of the intermediate layer 3 at 1050°C or lower, and even more preferable to perform it at 1000°C or lower. This is because the lower the firing temperature of the intermediate layer 3, the more effectively the electrochemical element E can be formed while suppressing damage and deterioration of the metal substrate 1. The order of the intermediate layer smoothing step and the intermediate layer firing step can also be reversed. The intermediate layer smoothing step can also be performed by performing lapping, leveling, surface cutting, polishing, etc.

[0122] (Electrolyte Layer Formation Step) In the electrolyte layer formation step, the electrolyte layer 4 is formed as a thin layer on the intermediate layer 3 while covering the electrode layer 2 and the intermediate layer 3. Alternatively, the electrolyte layer 4 may be formed as a thin film having a thickness of 10 μm or less. As described above, the electrolyte layer 4 is preferably formed by a low-temperature firing method (a wet method in which firing is performed at a low temperature of 1100°C or less). However, for example, the electrolyte layer 4 can be formed by applying the coating composition b2 according to the present invention by air spraying, bar coating, dispenser coating, brush coating, or spatula coating, followed by firing at a temperature of 1100°C or less. Other methods that can be used include spray coating (thermal spraying, aerosol deposition, aerosol gas deposition, powder jet deposition, particle jet deposition, cold spray, etc.), PVD (sputtering, pulsed laser deposition, etc.), and CVD. Regardless of which method is used, it is preferable to perform the process at a temperature of 1100°C or less to prevent deterioration of the metal substrate 1.

[0123] In order to form a high-quality electrolyte layer 4 that is dense and has high airtightness and gas barrier properties in a temperature range of 1100° C. or less, it is desirable to use the coating composition b2 according to the present invention in the electrolyte layer formation step and perform a low-temperature baking method. In this case, the electrolyte layer 4 can be formed by applying the material for the electrolyte layer 4 onto a base layer by an air spray method or the like, and then baking at a temperature of 1100° C. or less.

[0124] (Reaction Prevention Layer Formation Step) In the reaction prevention layer formation step, the reaction prevention layer 5 is formed as a thin layer on the electrolyte layer 4. As described above, the reaction prevention layer 5 can be formed by a low-temperature firing method, a spray coating method (such as thermal spraying, aerosol deposition, aerosol gas deposition, powder jet deposition, particle jet deposition, or cold spray), a PVD method (such as sputtering or pulsed laser deposition), or a CVD method. Whichever method is used, it is preferable to perform the process at a temperature of 1100°C or less to suppress deterioration of the metal substrate 1. Note that, in order to flatten the upper surface of the reaction prevention layer 5, for example, a leveling process, a cutting process, or a polishing process may be performed on the surface after the formation of the reaction prevention layer 5, or a press process may be performed after wet formation and before firing.

[0125] (Counter Electrode Layer Forming Step) In the counter electrode layer forming step, the counter electrode layer 6 is formed in a thin layer state on the reaction prevention layer 5. As described above, the counter electrode layer 6 can be formed by a low-temperature firing method, a spray coating method (such as a thermal spraying method, an aerosol deposition method, an aerosol gas deposition method, a powder jet deposition method, a particle jet deposition method, or a cold spray method), a PVD method (such as a sputtering method or a pulsed laser deposition method), or a CVD method. Whichever method is used, it is preferable to perform the method at a temperature of 1100° C. or less in order to suppress deterioration of the metal substrate 1.

[0126] In this manner, it is possible to manufacture the electrochemical element E. Incidentally, by carrying out the electrode layer forming step and intermediate layer forming step described above, it is possible to manufacture a substrate with an electrode layer for a metal-supported electrochemical element.

[0127] The electrochemical element E may be configured to have either or both of the intermediate layer 3 and the reaction prevention layer 5. That is, the electrode layer 2 and the electrolyte layer 4 may be formed in contact with each other, or the electrolyte layer 4 and the counter electrode layer 6 may be formed in contact with each other. In this case, the intermediate layer forming step and the reaction prevention layer forming step are omitted from the above-described manufacturing method.

[0128] [Electrochemical Element, Electrochemical Module, Electrochemical Device, Energy System] Using Figures 32 and 33, an example of a solid oxide fuel cell will be described for an electrochemical element E, an electrochemical module M, an electrochemical device Y, and an energy system Z. In this form of electrochemical element E, as shown in Figure 32, a U-shaped member 7 is attached to the back surface of a metal substrate 1, and the metal substrate 1 and the U-shaped member 7 form a cylindrical support TS. The U-shaped member 7 (separator) can be made of the same material as the metal substrate 1 (an alloy material having an Fe—Cr alloy base and a Co composite oxide coating on its outer surface). When the electrochemical element E is used as a fuel cell, the flow path formed between the metal substrate 1 and the U-shaped member 7 serves as a supply path for a reducing gas (typically, a fuel gas containing hydrogen). As shown in Figure 32, a plurality of electrochemical elements E are stacked with a current collecting member 26 sandwiched therebetween to form an electrochemical module M. Here, a stack is an example of an assembly. The current collecting member 26 is joined to the counter electrode layer 6 of the electrochemical element E and the U-shaped member 7, electrically connecting them together. Therefore, the electrochemical module M is electrically connected as a whole in the stacking direction. The current collecting member 26 can also be made of the same material as the metal substrate 1 (an alloy material having an Fe-Cr alloy base material and a Co-containing complex oxide coating on its outer surface). The above-mentioned alloy member is used.

[0129] As shown in Fig. 33, the electrochemical module M has a gas manifold 17, a terminal member m1, and a current draw-out portion m2. In the electrochemical element E, which is stacked with a current collecting member 26 sandwiched therebetween as shown in Fig. 32, one open end of the cylindrical support TS is connected to the gas manifold 17, and gas (in this example, reformed gas reformed by the reformer 34) is supplied from the gas manifold 17. The supplied gas flows through the inside of the cylindrical support TS and passes through the through-holes 1a of the metal substrate 1 to be supplied to the electrode layer 2.

[0130] 33 shows an overview of an energy system Z and an electrochemical device Y. The energy system Z includes an electrochemical device Y and a heat exchanger 53 as a waste heat utilization unit that reuses heat discharged from the electrochemical device Y. The electrochemical device Y includes an electrochemical module M, a fuel supply unit that has a desulfurizer 31 and a reformer 34 and supplies a fuel gas containing a reducing gas to the electrochemical module M, and an inverter 38 as a power conversion unit that extracts electric power from the electrochemical module M. Therefore, the electrochemical device Y is a power generation device that generates electric power when fuel is supplied.

[0131] More specifically, the electrochemical device Y includes a desulfurizer 31, a reforming water tank 32, a vaporizer 33, a reformer 34, a blower 35, a combustion unit 36, an inverter 38, a control unit 39, a storage container 40, and an electrochemical module M.

[0132] The desulfurizer 31 removes (desulfurizes) sulfur compounds contained in hydrocarbon raw fuel such as city gas. When sulfur compounds are contained in the raw fuel, the provision of the desulfurizer 31 can suppress the effects of the sulfur compounds on the reformer 34 or the electrochemical element E. The vaporizer 33 generates steam from reforming water supplied from the reforming water tank 32. The reformer 34 uses the steam generated in the vaporizer 33 to steam reform the raw fuel desulfurized in the desulfurizer 31, thereby generating a reformed gas containing hydrogen.

[0133] The electrochemical module M generates electricity by electrochemical reaction using the reformed gas supplied from the reformer 34 and air supplied from the blower 35. The combustion section 36 mixes the reaction exhaust gas discharged from the electrochemical module M with air and combusts combustible components in the reaction exhaust gas.

[0134] The electrochemical module M has a plurality of electrochemical elements E and a gas manifold 17. The plurality of electrochemical elements E are arranged in parallel while electrically connected to each other, and one end (lower end) of each electrochemical element E is fixed to the gas manifold 17. The electrochemical elements E generate electricity by electrochemically reacting the reformed gas supplied through the gas manifold 17 with air supplied from the blower 35.

[0135] The inverter 38 adjusts the output power of the electrochemical module M to the same voltage and frequency as the power received from a commercial grid (not shown). Thus, the inverter 38 serves as a power converter that extracts power from the electrochemical element E or the electrochemical module M. The control unit 39 controls the operation of the electrochemical device Y and the energy system Z.

[0136] The vaporizer 33, the reformer 34, the electrochemical module M, and the combustion section 36 are housed in a housing 40. The reformer 34 uses combustion heat generated by the combustion of the reaction exhaust gas in the combustion section 36 to carry out a reforming process of the raw fuel.

[0137] The raw fuel is supplied to the desulfurizer 31 through a raw fuel supply path 42 by operation of a booster pump 41. The reforming water in the reforming water tank 32 is supplied to the vaporizer 33 through a reforming water supply path 44 by operation of a reforming water pump 43. The raw fuel supply path 42 merges with the reforming water supply path 44 at a location downstream of the desulfurizer 31, and the reforming water and raw fuel that have merged outside the storage container 40 are supplied to the vaporizer 33 provided inside the storage container 40.

[0138] The reforming water is vaporized in the vaporizer 33 to become water vapor. The raw fuel containing water vapor produced in the vaporizer 33 is supplied to the reformer 34 through a water vapor-containing raw fuel supply path 45. The raw fuel is steam reformed in the reformer 34 to produce a reformed gas containing hydrogen gas as a main component (fuel gas containing hydrogen, which is a reducing gas as described above). The reformed gas produced in the reformer 34 is supplied to the gas manifold 17 of the electrochemical module M through a reformed gas supply path 46.

[0139] The reformed gas supplied to the gas manifold 17 is distributed to the plurality of electrochemical elements E and supplied to the electrochemical elements E from the lower end, which is the connection between the electrochemical elements E and the gas manifold 17. Mainly hydrogen in the reformed gas is used for the electrochemical reaction in the electrochemical elements E. Therefore, this reformer 34 serves as a fuel converter that supplies gas containing a reducing gas to the electrochemical elements E or the electrochemical modules M. Reaction exhaust gas containing the remaining hydrogen gas not used in the reaction is discharged from the upper end of the electrochemical elements E to the combustion section 36.

[0140] The reaction exhaust gas is combusted in the combustion section 36 to become combustion exhaust gas, which is discharged to the outside of the storage container 40 through a combustion exhaust gas outlet 50. A combustion catalyst section 51 (e.g., a platinum-based catalyst) is arranged in the combustion exhaust gas outlet 50, and combusts and removes reducing gases such as carbon monoxide and hydrogen contained in the combustion exhaust gas. The combustion exhaust gas discharged from the combustion exhaust gas outlet 50 is sent to a heat exchanger 53 through a combustion exhaust gas discharge path 52.

[0141] The heat exchanger 53 exchanges heat between the combustion exhaust gas generated by combustion in the combustion section 36 and the supplied cold water to generate hot water. That is, the heat exchanger 53 operates as a waste heat utilization section that reuses the heat discharged from the electrochemical device Y.

[0142] Instead of the exhaust heat utilization section, a reaction exhaust gas utilization section (not shown) may be provided that utilizes the reaction exhaust gas discharged (without being burned) from the electrochemical module M. The reaction exhaust gas contains the remaining hydrogen gas that was not used in the reaction in the electrochemical element E. In the reaction exhaust gas utilization section, the remaining hydrogen gas is utilized for heat utilization by combustion or for power generation using a fuel cell or the like, thereby making effective use of energy.

[0143] 34 shows another embodiment of the electrochemical module M. The electrochemical module M according to this another embodiment is configured by stacking the above-described electrochemical elements E with inter-cell connection members 71 sandwiched therebetween.

[0144] The inter-cell connection member 71 is a plate-shaped member that is electrically conductive and gas impermeable, and has grooves 72 formed on the front and back surfaces that are perpendicular to each other. The inter-cell connection member 71 can be made of a metal such as stainless steel or a metal oxide.

[0145] 34 , when electrochemical elements E are stacked with this inter-cell connection member 71 sandwiched therebetween, gas can be supplied to the electrochemical elements E through the grooves 72. More specifically, one groove 72 serves as a first gas flow path 72a, which supplies gas to the front side of the electrochemical element E, i.e., the counter electrode layer 6. The other groove 72 serves as a second gas flow path 72b, which supplies gas to the back side of the electrochemical element E, i.e., the back surface of the metal substrate 1, through the through-holes 1a to the electrode layer 2.

[0146] When this electrochemical module M is operated as a fuel cell, an oxidizing gas (typically, air containing oxygen) is supplied to the first gas flow path 72a, and a reducing gas (typically, fuel gas containing hydrogen) is supplied to the second gas flow path 72b. This causes a reaction as a fuel cell to proceed in the electrochemical elements E, generating electromotive force and current. The generated power is extracted from the electrochemical module M through the inter-cell connecting members 71 at both ends of the stacked electrochemical elements E.

[0147] In this embodiment, grooves 72 that are perpendicular to each other are formed on the front and back surfaces of the inter-cell connection member 71, but grooves 72 that are parallel to each other can also be formed on the front and back surfaces of the inter-cell connection member 71.

[0148] [Other Embodiments] (1) In the above embodiment, the electrochemical element E is used in a solid oxide fuel cell. However, the electrochemical element E can also be used in a solid oxide electrolysis cell that causes an electrolytic reaction, an oxygen sensor that uses a solid oxide, or the like.

[0149] An example of using the electrochemical element E as a solid oxide electrolysis cell will be described below with reference to the drawings. As previously mentioned, in this example, the electrochemical device Y according to the present invention is used as a hydrocarbon production system 100, and the electrochemical element E is made to function as an electrolysis reaction section 10 by supplying predetermined raw material gas and electric power. That is, water H ２ O and carbon dioxide CO２ These are decomposed to produce carbon monoxide (CO) and hydrogen (H) as raw materials for synthesizing hydrocarbons. ２ Then, hydrocarbons can be obtained in the hydrocarbon synthesis reaction section 30.

[0150] FIG. 35 is a system diagram showing the overall configuration of the hydrocarbon production system 100, and FIG. 36 shows an example of the configuration of an electrolysis cell unit U that constitutes the hydrocarbon production system 100.

[0151] As can be seen from FIG. 35, the hydrocarbon production system 100 includes an electrolysis reaction section 10, a first catalytic reaction section 20, a second catalytic reaction section 30, a heavy hydrocarbon separation section 70 (illustrated as a CnHm separation section), a water separation section 80 (illustrated as a H ２ O separation section) and carbon dioxide separation section 90 (CO ２ 35, the electrolytic reaction section 10, the first catalytic reaction section 20, and the second catalytic reaction section 30 are depicted separately, but as shown in FIG. 36, these sections 10, 20, and 30 can be provided as a single electrolytic cell unit U.

[0152] The electrolysis reaction section 10 is a section where at least a part of the inflowing gas is electrolyzed, the first catalytic reaction section 20 is a reverse water-gas shift reaction section where at least a part of the inflowing gas undergoes a reverse water-gas shift reaction, and the second catalytic reaction section 30 is a hydrocarbon synthesis reaction section where at least a part of the inflowing gas is synthesized into hydrocarbons. ４ The primary hydrocarbons synthesized in the second catalytic reaction section 30 are hydrocarbons with one carbon atom (carbon number 1), but may also include lower saturated hydrocarbons with two to four carbon atoms. Furthermore, hydrocarbons with a carbon number greater than that of the lower saturated hydrocarbons and that are not saturated are also synthesized. These heavy hydrocarbons can be collected and separated in the heavy hydrocarbon separation section 70 as the gas released from the second catalytic reaction section 30 is cooled.

[0153] The water separation unit 80 and the carbon dioxide separation unit 90 separate predetermined components (H ２ O and CO ２The components removed and recovered by these sections are returned to a predetermined section of the system via a water return line 81 and a carbon dioxide return line 91 as shown in the figure, and are reused. ２ O and CO ２ As a result, the hydrocarbon production system 100 is substantially CO ２ This is a carbon closed system that does not release any gas outside the system. In the figure, the gas flowing into each part is shown before each part, and the gas released from that part is shown after.

[0154] In the electrolysis reaction section 10, H ２ O and CO ２ is introduced and electrolyzed inside, ２ O is H ２ and O2, and some CO ２ CO and O ２ The reaction is described as follows: ２ O → 2H ２ +O ２ (Formula 1) 2CO ２ →2CO+O ２ (Equation 2) These equations 1 and 2 are also shown in the box representing the electrolytic reaction section 10 in FIG.

[0155] In the first catalytic reaction section 20 (reverse water gas shift reaction section), at least H ２ and CO ２ is introduced, the reverse water gas shift reaction occurs inside, and CO ２ CO, H ２ is released as HO. The reaction is described as the following equilibrium reaction, but the reverse water gas shift reaction is a reaction in which the reaction described in Equation 3 below proceeds to the right (CO ２ and H ２ reacts to form CO and H ２ The reaction proceeds in the direction of producing CO. ２ +H ２ ⇔CO + H ２O (Equation 3) This equation 3 is also shown in the box representing the first catalytic reaction section 20 (reverse water gas shift reaction section) in Figure 35. The box also schematically shows the reverse water gas shift catalyst cat1 used in the reaction. The inventors believe that this type of reverse water gas shift catalyst cat1 is preferably a catalyst in which one or both of nickel and iron are supported as catalytically active components ca1 (metal catalysts) on one or more supports cb1 (metal oxide supports) selected from ceria-based metal oxides, zirconia-based metal oxides, and alumina-based metal oxides.

[0156] In the second catalytic reaction section 30 (hydrocarbon synthesis reaction section), at least H ２ and CO are introduced and hydrocarbons are synthesized through a catalytic reaction. ２ From CH ４ The reaction by which CO and H are synthesized is described as the following equilibrium reaction. ２ From CH ４ The reaction in which is synthesized is the reaction described in the following formula 4, which proceeds to the right (CO and H2 react to form CH ４ and H ２ The reaction proceeds in the direction of producing O. ２ ⇔CH ４ +H ２ O (Equation 4) This equation 4 is also shown in the box representing the second catalytic reaction section 30 (hydrocarbon synthesis reaction section) in FIG. 35. The box also shows a schematic representation of the hydrocarbon synthesis catalyst cat2 used in the reaction. The inventors believe that this type of hydrocarbon synthesis catalyst cat2 is preferably a catalyst in which at least ruthenium, as the catalytically active component ca2, is supported on a carrier cb2 (metal oxide carrier), such as alumina. Furthermore, the equilibrium reaction of (Equation 3) also occurs at this site. Depending on the type of catalyst used in the second catalytic reaction section 30, it is possible to proceed with the FT (Fischer-Tropsch) synthesis reaction, so that CO and H ２ It is also possible to synthesize hydrocarbons such as ethane and propane from this.

[0157] H generated in the water separation section 80 ２O is separated and returned to the upstream side of the electrolysis reaction unit 10 via a water return line 81 (water recycle line). ２ is separated and returned to the upstream side of the electrolysis reaction section 10 via a carbon dioxide return line 91 (carbon dioxide recycle line). As a result, in this hydrocarbon production system 100, hydrocarbons are ultimately synthesized and can be supplied to the outside.

[0158] An electrolytic cell unit U having such an electrochemical element E in the electrolytic reaction section 10 and also equipped with a reverse water gas shift reaction section 20 and a hydrocarbon synthesis reaction section 30 is shown in Figure 36. Figure 36 is a diagram illustrating the electrolytic cell unit U, including the direction of gas advection. In order to clarify the electrochemical reaction system, the intermediate layer 3 and reaction prevention layer 5 of the electrochemical element E shown in Figure 31 are omitted from this figure. Furthermore, in comparison with Figure 35, the heavy hydrocarbon separation section 70, water separation section 80, and carbon dioxide separation section 90 are omitted.

[0159] This electrolysis cell unit U also includes an electrochemical element E in which an electrode layer 2 and a counter electrode layer 6 are formed with an electrolyte layer 4 sandwiched therebetween, a metal substrate 1 serving as a metal support and acting as a separator, a U-shaped member 7 serving as a supply path forming member, and a current collecting member 26 serving as a supply path forming member, and is configured to form an electrode layer side gas supply path 7a and a counter electrode layer side gas supply path 26a. ２ O and CO ２ On the other hand, air g2 (O ２ ) is supplied. The electrochemical module M can be constructed by stacking (assembling) these electrolytic cell units U in the unit thickness direction, which is the left-right direction in FIG. 36 . As described above, the coating composition b2 according to the present invention can be used to construct the electrolyte layer 4 and, as a part thereof, the electrode layer 2.

[0160] This alternative configuration is an example in which an electrochemical element E functions as an electrolytic reaction unit 10. As can be seen from FIG. 36 , DC power is supplied between the electrode layer 2 and the counter electrode layer 6. The illustrated example shows an example in which power obtained from an AC power source 37 is converted to AC / DC by an inverter 38 and supplied to the electrochemical element E. Therefore, the inverter 38 functions as a power converter that supplies power to the electrochemical element E or, when an electrochemical element E is integrated, to the electrochemical module M, which is an assembly of the electrochemical element E. However, a reverse water gas shift catalyst cat1 is applied to the inner surface of the electrode layer-side gas supply channel 7a (the inner surface of the U-shaped member 7 on the supply channel side, the surface of the metal substrate 1 opposite the surface on which the electrode layer 2 is formed, and the surfaces of the multiple through-holes 1a). This coating layer 20b is indicated by a thick solid line. Furthermore, the electrode layer-side gas supply channel 7a extends beyond the electrolytic reaction unit 10, and the coating layer 20b is also provided on this extension. Furthermore, a hydrocarbon synthesis catalyst cat2 is applied to the tip of the catalyst layer 30b to form the hydrocarbon synthesis reaction section 30. As a result, in this configuration, the hydrocarbon synthesis reaction section 30 serves as a power converter that supplies power to the electrochemical elements E or, when these are integrated, to the electrochemical module M, which is an assembly of these elements. Then, hydrocarbons can be obtained in the hydrocarbon synthesis reaction section 30 using the gases obtained in the electrolysis reaction section 10 and the reverse water gas shift reaction section 20.

[0161] (2) In the above embodiment, the present invention is used in a metal-supported solid oxide fuel cell using the metal substrate 1 as the support, but the present invention can also be used in an electrode-supported solid oxide fuel cell using the electrode layer 2 or the counter electrode layer 6 as the support, or an electrolyte-supported solid oxide fuel cell using the electrolyte layer 4 as the support. In these cases, the electrode layer 2 or the counter electrode layer 6, or the electrolyte layer 4 can be made to have a required thickness so that it can function as a support.

[0162] (3) In the above embodiment, the material of the electrode layer 2 is, for example, NiO-GDC, Ni-GDC, NiO-YSZ, Ni-YSZ, or CuO-CeO ２ , Cu—CeO ２A composite material such as LSCF or LSM is used, and a composite oxide such as LSCF or LSM is used as the material for the counter electrode layer 6. The electrochemical element E configured in this manner can be used as a solid oxide fuel cell by supplying hydrogen gas to the electrode layer 2 to make it a fuel electrode and by supplying air to the counter electrode layer 6 to make it an air electrode. This configuration can also be modified to configure the electrochemical element E so that the electrode layer 2 can be made to be an air electrode and the counter electrode layer 6 can be made to be a fuel electrode. That is, a composite oxide such as LSCF or LSM is used as the material for the electrode layer 2, and a composite oxide such as NiO-GDC, Ni-GDC, NiO-YSZ, Ni-YSZ, or CuO-CeO is used as the material for the counter electrode layer 6. ２ , Cu—CeO ２ In the electrochemical element E configured in this manner, air is supplied to the electrode layer 2 to serve as an air electrode, and hydrogen gas is supplied to the counter electrode layer 6 to serve as a fuel electrode, so that the electrochemical element E can be used as a solid oxide fuel cell.

[0163] (4) In the above embodiment, an example was shown in which a composite oxide coating containing Co was formed on the surface of the Fe—Cr alloy of the metal substrate 1 to suppress volatilization of Cr and other elements from this material. However, one or more of the U-shaped member 7 serving as a separator, the gas manifold 17, the current collecting member 26, and the inter-cell connecting member 71 serving as an interconnector may be made of this type of alloy member. Alternatively, this type of oxide coating may be an oxide coating of only Co formed on the surface of an Fe—Cr alloy. This is effective against volatilization of Cr.

[0164] The configurations disclosed in the above embodiments can be applied in combination with configurations disclosed in other embodiments as long as no contradiction occurs. Furthermore, the embodiments disclosed in this specification are merely examples, and the present invention is not limited to these, and can be modified as appropriate within the scope of the object of the present invention.

[0165] The present invention is suitable for use in a method for producing a coating composition that can form a film at low cost by a simple method using zirconium alkoxide and an yttrium compound as starting materials, and that can also produce an yttria-stabilized zirconia layer with few defects such as cracks, an yttria-stabilized zirconia layer, an electrochemical element, an electrochemical module, an electrochemical device, an energy system, a solid oxide fuel cell, and a solid oxide electrolysis cell.

[0166] REFERENCE SIGNS LIST 1 Metal substrate (metal support) 1a Through-hole 2 Electrode layer 3 Intermediate layer 4 Electrolyte layer 5 Reaction prevention layer 6 Counter electrode layer 7 U-shaped member (separator) 10 Electrolysis reaction section 17 Gas manifold (manifold) 20 First catalytic reaction section (reverse water gas shift reaction section) 26 Current collecting member 30 Second catalytic reaction section (hydrocarbon synthesis reaction section, fuel converter) 31 Desulfurizer 32 Reforming water tank 33 Vaporizer 34 Reformer (fuel converter) 35 Blower 36 Combustion section 38 Inverter (power converter) 39 Control section 40 Storage container 41 Booster pump 42 Raw fuel supply channel 43 Reforming water pump 44 Reforming water supply channel 45 Steam-containing raw fuel supply channel 46 Reformed gas supply channel 50 Combustion exhaust gas outlet 51 Combustion catalyst section 52 Combustion exhaust gas discharge path 53 Heat exchanger (exhaust heat utilization section) 70 Heavy hydrocarbon separation section 71 Inter-cell connection member (interconnector) 72 Groove 72a First gas flow path 72b Second gas flow path 80 Water separation section 90 Carbon dioxide separation section 100 Hydrocarbon production system E Electrochemical element M Electrochemical module TS Cylindrical support U Electrolysis cell unit Y Electrochemical device Z Energy system o Zirconium alkoxide p Yttrium compound q Chelate compound r Polyalkylene glycol s Catalyst t Water u Organic solvent

Claims

1. A method for producing a coating composition, comprising mixing a composition containing a zirconium alkoxide, an yttrium compound, a chelate compound, a polyalkylene glycol, a catalyst, water, and an organic solvent to produce a coating composition.

2. A method for producing a coating composition according to claim 1, wherein the coating composition contains zirconium alkoxide at 10 to 30% by mass, yttrium compound at 1 to 10% by mass, chelate compound at 3 to 15% by mass, polyalkylene glycol at 0.3 to 7% by weight, catalyst at 0.1 to 2% by mass, water at 0.1 to 2% by mass, and organic solvent at the balance.

3. A method for producing a coating composition according to claim 1 or 2, wherein the zirconium alkoxide is one or more of zirconium (IV) methoxide, zirconium (IV) ethoxide, zirconium (IV) n-propoxide, zirconium (IV) i-propoxide, zirconium (IV) n-butoxide, zirconium (IV) i-butoxide, zirconium (IV) sec-butoxide, and zirconium (IV) t-butoxide.

4. A method for producing a coating composition according to any one of claims 1 to 3, wherein the yttrium compound is one or more of yttrium nitrate, yttrium chloride, yttrium sulfate, yttrium phosphate, yttrium acetate, yttrium carbonate, yttrium (III) ethoxide, yttrium (III) n-propoxide, and yttrium (III) i-propoxide.

5. The method for producing a coating composition according to any one of claims 1 to 4, wherein the chelate compound is represented by the general formula (1). １ -CO-CH ２ -C-O-R ２ General formula (1): [In the formula, R1 and R2 are an alkyl group having 1 to 6 carbon atoms (including a fluorinated alkyl group), or a monocyclic or bicyclic aryl group; R1 and R2 may be the same or different and each is an alkyl group having 1 to 6 carbon atoms, or a monocyclic or bicyclic aryl group. R1 and R2 may be linked to each other to form a cyclic alkyl group.] 6. A method for producing a coating composition according to any one of claims 1 to 5, wherein the chelating compound is one or more of 2,4-pentanedione, 2,4-hexanedione, 3,5-heptanedione, 2,6-dimethyl-3,5-heptanedione, 2,2,6,6-tetramethyl-3,5-heptanedione, 1-phenyl-1,3-butanedione, 1,3-diphenyl-1,3-propanedione, 1,1,1-trifluoro-2,4-pentanedione, 1,1,1,5,5,5-hexafluoro-2,4-pentanedione, and 1,3-cyclohexanedione.

7. A method for producing a coating composition described in any one of claims 1 to 6, wherein the polyalkylene glycol is one or more of tetraethylene glycol, pentaethylene glycol, polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 600, polyethylene glycol 1000, tripropylene glycol, tetrapropylene glycol, polypropylene glycol 400, polypropylene glycol 700, and polypropylene glycol 1000.

8. A method for producing a coating composition according to any one of claims 1 to 7, wherein the catalyst is one or more of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, carbonic acid and acetic acid.

9. A method for producing a coating composition according to any one of claims 1 to 8, wherein the organic solvent is one or more of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, and 2-methyl-2-propanol.

10. A yttria-stabilized zirconia layer obtained by curing a coating composition produced by the method for producing a coating composition according to any one of claims 1 to 9.

11. An electrochemical element comprising the yttria-stabilized zirconia layer according to claim 10.

12. The electrochemical device according to claim 11, which has a metal support.

13. An electrochemical module in which a plurality of electrochemical elements according to claim 11 or 12 are arranged in an assembled state.

14. An electrochemical device comprising: an electrochemical element according to claim 11 or 12; or an electrochemical module according to claim 13; and a fuel converter which supplies a gas containing a reducing gas to the electrochemical element or the electrochemical module, or a fuel converter which converts a gas containing a reducing gas generated in the electrochemical element or the electrochemical module.

15. An electrochemical device comprising at least the electrochemical element according to claim 11 or 12 or the electrochemical module according to claim 13, and a power converter for extracting power from the electrochemical element or the electrochemical module, or a power converter for supplying power to the electrochemical element or the electrochemical module.

16. An energy system comprising the electrochemical device according to claim 14 or 15, and a waste heat utilization section for reusing heat discharged from the electrochemical device.

17. A solid oxide fuel cell comprising the electrochemical element according to claim 11 or 12, in which a power generation reaction occurs in said electrochemical element.

18. A solid oxide electrolysis cell comprising the electrochemical element according to claim 11 or 12, in which an electrolytic reaction occurs.

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