Method for producing yttria-stabilized zirconia layer, method for producing electrochemical element, method for producing solid oxide fuel battery, and method for producing solid oxide fuel battery cell

Abstract

To obtain a dense yttria-stabilized zirconia layer.SOLUTION: An yttria-stabilized zirconia layer is obtained by applying a coating composition to the surface of a target object and curing it, wherein the coating composition is prepared by mixing a composition containing, as raw materials, zirconium acetate, an yttrium compound, a chelating compound, a catalyst, water, and an organic solvent, and wherein the content of zirconium acetate in the coating composition is 10 to 30 mass%, the content of the yttrium compound is 1 to 10 mass%, the content of the chelating compound is 3 to 10 mass%, the content of the catalyst is 0.1 to 2 mass%, the content of water is 5 to 15 mass%, and the content of the organic solvent is the balance.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[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. [Background technology]

[0002] It has been known that yttria-stabilized zirconia (hereinafter sometimes referred to as YSZ) is coated on the surface of various components and used in parts that require high hardness and inertness, as well as refractory parts used in jet engines, etc. It is also known to be used as a solid electrolyte in solid oxide fuel cells (SOFCs), which are used at relatively high temperatures. The following technologies are examples of applications of YSZ as a solid electrolyte in SOFCs.

[0003] 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.

[0004] Here, it is said that in addition to 1-propanol, 2-propanol and 2-methyl-1-propanol are also suitable as the first solvent, and furthermore, benzene, hexane, methanol, ethanol, etc. can also be used.

[0005] 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 be used.

[0006] Patent Document 2 discloses a ceramic material containing truncated conical tubular pores, which is produced by orientation-freezing a slip consisting of ceramic powder such as yttria-stabilized zirconia, zirconium acetate as a crystal growth promoter, polyvinyl alcohol, polyethylene glycol or cellulose as a temporary binder, and water, to obtain a porous preform, which is then sintered at 1350 to 1400°C.

[0007] Non-Patent Document 3 discloses a zirconia thin film obtained by dip-coating a heat-resistant glass substrate in an aqueous solution of zirconium acetate and baking the resulting substrate at 600°C. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 7-235317 [Patent Document 2] Patent No. 5965897 [Non-patent document 3] Journal of the Ceramic Society of Japan 114[5]414-415(2006) Summary of the Invention [Problem to be solved by the invention]

[0009] However, it has been found that the technology disclosed in Patent Document 1 has the following problems. (1) When attempting to form the yttria-stabilized zirconia as an electrolyte layer on the surface of an air electrode formed from a porous metal oxide, the formed body is immersed in a coating solution and the dipping process is repeated to obtain an yttria-stabilized zirconia coating. In order to obtain an yttria-stabilized zirconia coating film with a thickness of about 1 μm, the dipping process must be repeated 20 times, which is inferior in terms of productivity.

[0010] (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.

[0011] (3) When this method is used, the entire surface of the coating film will have a rough, granular appearance, and the coating film will easily peel off even with a light touch of a finger, which may result in the coating film not being able to reach the required baking stage after formation.

[0012] Furthermore, the technology disclosed in Patent Document 2 has a complicated manufacturing process, requiring a final sintering process at a high temperature of 1350 to 1400° C. Furthermore, since the obtained substance is a bulk solid, it is difficult to arrange or fix it on a metal substrate, and there are problems with adhesion to the substrate.

[0013] Furthermore, the technology disclosed in Non-Patent Document 3 uses an aqueous solution of zirconium acetate as a starting material and repeats the dipping process three times to obtain a zirconia layer with a film thickness of 100 nm (0.1 μm). Therefore, to obtain a film thickness of 1 μm, the dipping process must be repeated 30 times, which is inferior in terms of productivity.

[0014] It is also stated that adding 0.1% by volume of a surfactant to an aqueous solution of zirconium acetate improved the wettability of the solution to a heat-resistant glass substrate. However, it is difficult to apply the aqueous solution of zirconium acetate uniformly to the substrate, and unevenness occurs during drying, which tends to result in a rough, uneven surface of the zirconia layer after firing.

[0015] 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 acetate and an yttrium compound as starting materials, and that can also provide a dense yttria-stabilized zirconia layer. [Means for solving the problem]

[0016] A first characteristic feature of the present invention is that the coating composition is produced by mixing zirconium acetate, an yttrium compound, a chelate compound, a catalyst, water, and an organic solvent.

[0017] The coating composition produced by this method contains water necessary for the hydrolysis of zirconium acetate, 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 by obtaining this coating film, a yttria-stabilized zirconia layer with few defects can be easily obtained when the coating composition of the present invention is used.

[0018] This coating composition uses zirconium acetate as its zirconium source, which is stable in air and inexpensive. Therefore, it is possible to stably obtain a coating film of yttria-stabilized zirconia that will become the yttria-stabilized zirconia layer. The stabilization of the manufacturing process allows for the mass production of high-quality, stable products. Therefore, productivity is significantly improved in terms of both quality and mass production.

[0019] The second characteristic configuration of the present invention is: The coating composition contains yttria-stabilized zirconia fine particles.

[0020] By adopting this configuration, the yttria-stabilized zirconia fine particles serve as a filler (aggregate) when forming the yttria-stabilized zirconia layer, making it easy to ensure the desired layer thickness. As will be described later, the layer thickness obtained after a given number of coating operations using a coating composition containing yttria-stabilized zirconia fine particles can be clearly thicker than the layer thickness obtained after the same number of coating operations using a coating composition that does not contain yttria-stabilized zirconia fine particles (see comparisons between Examples 1 and 2 and between Examples 3 and 4, described later). Furthermore, the addition of yttria-stabilized zirconia fine particles is expected to relieve stress within the yttria-stabilized zirconia layer, thereby preventing defects such as cracks.

[0021] The third characteristic configuration of the present invention is The content of the yttria-stabilized zirconia fine particles is 1 to 10 mass % relative to the zirconium acetate.

[0022] That is, by adjusting the ratio (mass ratio) of yttria-stabilized zirconia fine particles to zirconium acetate to 1 to 10 mass%, the contained fine particles can function as a filler. Here, if the amount is less than 1 mass%, the effect of adding the fine particles may be difficult to obtain. On the other hand, if the amount is more than 10 mass%, the action of the raw materials that contribute to the original layer formation may be disrupted, and the uniformity and dispersibility in the coating composition may be deteriorated.

[0023] A fourth characteristic configuration of the present invention is as follows: The yttria-stabilized zirconia fine particles have an average particle size of 0.1 to 2 μm.

[0024] The average particle size of the yttria-stabilized zirconia particles is preferably 0.1 to 2 μm. If the average particle size is smaller than 0.1 μm, the particles may aggregate in the coating composition, impairing dispersibility and uniformity, while if the average particle size is larger than 2 μm, problems such as poor coating film smoothness and uneven distribution in the coating film may occur.

[0025] A fifth characteristic configuration of the present invention is The coating composition contains 10 to 30% by mass of zirconium acetate, 1 to 10% by mass of the yttrium compound, 3 to 10% by mass of the chelate compound, 0.1 to 2% by mass of the catalyst, 5 to 15% by mass of the water, and the remainder of the organic solvent.

[0026] If the zirconium acetate content is less than 10% by mass, the raw material tends to be insufficient, delaying the production of the target product. On the other hand, if it is more than 30% by mass, hydrolysis and condensation may proceed too quickly.

[0027] 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.

[0028] 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 zirconium acetate, whereas if it is more than 10% by mass, the hydrolysis rate and polycondensation rate are likely to be excessively suppressed.

[0029] The catalyst is used to uniformly initiate the hydrolysis of zirconium acetate and at the same time as a deflocculating agent to uniformly disperse the sol produced by the hydrolysis. If the content is less than 0.1% by mass, the function may not be fully exerted, and if it is added in excess of 2% by mass, no further effect will be obtained.

[0030] Water is used to dissolve and hydrolyze zirconium acetate. The amount of water added is preferably about 5 to 15 moles per mole of zirconium acetate. The content of water in the coating composition is preferably 5 to 15 mass %. However, as described below, if an aqueous solution of zirconium acetate is used, both zirconium acetate and water can be supplied.

[0031] Because water is used to dissolve and hydrolyze zirconium acetate, if the amount is less than 5 moles, the composition will not be able to achieve its purpose of promoting the hydrolysis reaction on its own. Adding more than 15 moles of water will not provide any additional benefits. From the standpoint of the coatability and ease of handling of the coating composition, a range of approximately 5 to 15 mass% is preferred.

[0032] When the yttria-stabilized zirconia fine particles are contained, the content thereof in the coating composition is preferably in the range of about 0.1 to 1 mass %.

[0033] As described in the sixth characteristic configuration of the present invention, Yttrium compounds are starting materials for yttria-stabilized zirconia, and include yttrium nitrate, yttrium chloride, yttrium sulfate, yttrium phosphate, yttrium acetate, yttrium carbonate, yttrium (III) ethoxide, yttrium (III) n-propoxide, and yttrium (III) i-propoxide.

[0034] When an inorganic acid salt is used for 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.

[0035] 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 a coating film of yttria-stabilized zirconia (yttria-stabilized zirconia layer) by reacting with the hydrolysis product of zirconium acetate.

[0036] As described in the seventh characteristic configuration of the present invention, The chelate compound is represented by the general formula (1). R1-CO-CH2-CO-R2 General formula (1) [In the formula, R1 and R2 are alkyl groups having 1 to 6 carbon atoms (including fluorinated alkyl groups), 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.]

[0037] This chelate compound coordinates with zirconium acetate and inhibits the hydrolysis and polycondensation rates of zirconium acetate.

[0038] As described in the eighth characteristic configuration of the present invention, Chelate compounds of this type 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.

[0039] 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 coordination ability with zirconium acetate. In these compounds, R1 and R2 are electron-donating groups such as methyl, ethyl, propyl, butyl, and phenyl groups, and therefore have excellent coordination ability with zirconium acetate, suppressing the hydrolysis reaction rate and polycondensation reaction rate of zirconium acetate, making it possible to obtain an yttria-stabilized zirconia coating film (yttria-stabilized zirconia layer) that is free from cracking and peeling.

[0040] As described in the ninth characteristic configuration of the present invention, As the catalyst, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, carbonic acid, and acetic acid can be used.

[0041] 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 acetate. By using these acids, zirconium acetate can be uniformly hydrolyzed and the resulting sol can be uniformly dispersed in the reaction solution, making it possible to obtain a coating film of yttria-stabilized zirconia (yttria-stabilized zirconia layer) that is free from cracks and peeling.

[0042] As described in the tenth characteristic configuration of the present invention, Examples of organic solvents include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, and 2-methyl-2-propanol. This is the balance of the other components (zirconium acetate, yttrium compound, chelate compound, catalyst, and water), and its content in the coating composition is preferably 40 to 80 mass % while satisfying the conditions of the other components. If the organic solvent content is less than 40% by mass, sufficient mixing performance may not be obtained, whereas if it is more than 80% by mass, the raw material components tend to be insufficient.

[0043] The alcohol is not particularly limited as long as it can dissolve zirconium acetate and the yttrium compound.

[0044] [Use of Yttria-Stabilized Zirconia Layer] The following describes the case where the yttria-stabilized zirconia layer according to the present invention is used in the "electrochemical element" of the present invention.

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

[0046] When this electrochemical device is used as a fuel cell, for example, the electrode layer can be used as a fuel electrode layer and the counter electrode layer can be used 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 device can be used as a single fuel cell. Conversely, when a predetermined amount of power is supplied between the two electrodes, the electrochemical element can function as an electrolytic element (electrolysis element) that receives a supply of water and decomposes it. Hereinafter, electrolysis may be referred to simply 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 allows for the easy production of an yttria-stabilized zirconia layer and can therefore 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, as described in the twelfth characteristic configuration of the present invention, the electrochemical element according to the present invention can be configured by including an yttria-stabilized zirconia layer.

[0050] Here, as described in the thirteenth characteristic configuration of the present invention, it is preferable that the electrochemical device has a metal support.

[0051] By adopting this configuration, the electrochemical elements can be supported by a robust metal support, and the required electrical conductivity between the electrochemical elements can be ensured.

[0052] As described in the fourteenth characteristic configuration of the present invention, an electrochemical module can be formed by assembling a plurality of the electrochemical elements described above.

[0053] According to this 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.

[0054] As described in a 15th characteristic configuration of the present invention, an electrochemical device can be configured having the above-mentioned electrochemical element or electrochemical module, and a fuel converter that circulates a gas containing a reducing gas through the electrochemical element or the electrochemical module, or a fuel converter that converts a gas containing a reducing component generated in the electrochemical element or the electrochemical module.

[0055] With this configuration, when the electrochemical element or electrochemical module is operated as a fuel cell, a fuel converter such as a reformer can be used to generate hydrogen from natural gas or the like supplied using existing raw fuel supply infrastructure such as city gas, and the hydrogen can be distributed to the fuel cell. Also, when the electrochemical element or electrochemical module is operated as an electrolysis cell, it can be an electrochemical device in which, for example, 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.

[0056] As described in the 16th characteristic configuration of the present invention, an electrochemical device can be configured that includes at least the above-mentioned electrochemical element or electrochemical module, and a power converter that extracts power from the electrochemical element or electrochemical module, or a power converter that distributes power to the electrochemical element or electrochemical module.

[0057] With this configuration, the power converter can convert the power extracted from the electrochemical element or electrochemical module and provide it for external use, or power can be supplied from the outside to both, allowing the electrochemical element or electrochemical module to be used for electrolysis. For example, using an inverter as the power converter is preferable because it can boost 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.

[0058] As described in the seventeenth characteristic configuration of the present invention, an energy system can be constructed that includes the electrochemical device described above and a waste heat utilization section that reuses the heat discharged from the electrochemical device.

[0059] According to the above characteristic configuration, since the electrochemical device and the waste heat utilization unit that reuses the heat discharged from the electrochemical device are included, an energy system that is excellent in durability, reliability, and performance, as well as energy efficiency, can be realized. Furthermore, it is also possible to realize a hybrid system with excellent energy efficiency by combining it with a power generation system that generates electricity by utilizing the combustion heat of unused fuel gas discharged from the electrochemical device.

[0060] As described as an 18th characteristic configuration of the present invention, a solid oxide fuel cell can be formed by providing electrochemical elements and causing a power generation reaction in these electrochemical elements.

[0061] On the other hand, as described in the 19th characteristic configuration of the present invention, a solid oxide electrolysis cell can be obtained by including the electrochemical elements described above and causing an electrolytic reaction in these electrochemical elements. [Brief explanation of the drawings]

[0062] [Figure 1] 1 shows the manufacturing process of a coating composition. [Figure 2] FIG. 1 shows the manufacturing process of a coating composition containing yttria-stabilized zirconia fine particles. [Figure 3] A diagram showing the state of coating of the coating composition [Figure 4] XRD measurement results of the coating film of Example 1 [Figure 5] XRD measurement results of the coating film of Example 2 [Figure 6] XRD measurement results of the coating film of Example 3 [Figure 7] XRD measurement results of the coating film of Example 4 [Figure 8] 1 is a cross-sectional view showing a configuration example of an electrochemical element; [Figure 9] A diagram showing an example of the configuration of an electrochemical module [Figure 10] FIG. 1 shows an example of the configuration of an electrochemical device that functions as a fuel cell device. [Figure 11] 1 is a cross-sectional view of a main part showing another example of the configuration of an electrochemical element; [Figure 12] FIG. 10 is a diagram showing another use of an electrochemical element in an electrolytic reaction section. [Figure 13] FIG. 10 is a diagram showing another embodiment equipped with an electrolysis reaction section, a reverse water gas shift reaction section, and a hydrocarbon synthesis reaction section. DETAILED DESCRIPTION OF THE INVENTION

[0063] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. Figures 1 and 2 show the manufacturing process of coating composition b2 according to the present invention, and an example of its application process is shown in Figure 3. 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 coating composition b2 contains yttria-stabilized zirconia fine particles Pa.

[0064] As explained above, the coating composition b2 produced by the coating composition production method according to the present invention contains a mixture of zirconium acetate o, yttrium compound p, chelate compound q, catalyst r, water s, and organic solvent t. Furthermore, yttria-stabilized zirconia fine particles Pa are added if necessary. Then, as shown in Figure 3, this coating composition b2 is applied to a predetermined position, dried, and baked to harden, resulting in an yttria-stabilized zirconia (YSZ) layer.

[0065] Zirconium acetate o may be in the form of powder, an acidic aqueous solution, a dilute acetic acid aqueous solution, etc. When an acidic aqueous solution or a dilute acetic acid aqueous solution is used, it is not necessary to add water to the coating composition b2. The content of zirconium acetate o in the coating composition b2 is preferably 10 to 30 mass %. In the examples and comparative examples described below, a dilute aqueous acetic acid solution of zirconium acetate is used.

[0066] 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 %. In the examples and comparative examples described below, examples using yttrium nitrate are shown.

[0067] Examples of the chelating 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 about 0.5 to 3 moles per mole of zirconium acetate, and the content of chelate compound q in coating composition b2 is preferably 3 to 10 mass %. In the examples and comparative examples described below, examples in which 2,4-pentanedione, 3,5-heptanedione, 2,6-dimethyl-3,5-heptanedione, and 2,2,6,6-tetramethyl-3,5-heptanedione are used are shown.

[0068] Examples of catalyst r that can be used include hydrochloric acid, acetic acid, nitric acid, sulfuric acid, and phosphoric acid. The content of catalyst r in coating composition b2 is preferably 0.1 to 2 mass %. In the examples and comparative examples described below, examples using nitric acid are shown.

[0069] Since water s is also used for the hydrolysis of zirconium acetate o, if the amount of water s is less than 0.25 moles per mole of zirconium acetate, the composition will not be able to independently promote the hydrolysis reaction, and if the amount is more than 4.0 moles, no additional effect will be obtained. From the viewpoint of the coatability and ease of handling of coating composition b2, the content of water s in coating composition b2 is preferably in the range of about 5 to 15 mass%.

[0070] Examples of organic solvents t include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, and 2-methyl-2-propanol. Organic solvent t represents the remaining amount of other components. In the following examples and comparative examples, 1-propanol is used.

[0071] Commercially available powder products can be used as the yttria-stabilized zirconia fine particles Pa. The content of the yttria-stabilized zirconia fine particles Pa in the coating composition b2 is preferably 1 to 10 mass% relative to the zirconium acetate o. The average particle size of the yttria-stabilized zirconia fine particles Pa is preferably 0.1 to 2 μm. From the viewpoints of the coatability and ease of handling of the coating composition b2, the content of the yttria-stabilized zirconia fine particles Pa in the coating composition b2 is preferably in the range of about 0.1 to 1 mass%.

[0072] [Examples and Comparative Examples] In the following Examples 1 to 4 and Comparative Examples 1 and 2, as shown in Figure 3, 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, with gadolinium-doped ceria b1 screen-printed on the surface), followed by heat treatment at a predetermined temperature for a predetermined time, to evaluate whether the 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 constitutes the electrochemical element E (see paragraphs

[106] to

[116] and Figure 8).

[0073] As an example of mixing, Figure 1 shows the state in which raw materials (zirconium acetate o, yttrium compound p, chelate compound q, catalyst r, water s, organic solvent t) are placed in a glass container V1 and mixed using a magnetic stirrer W1 (Figures (a) and (b)). Figure 2 shows an example in which a mixture of yttria-stabilized zirconia particles Pa and organic solvent t is first prepared using a vibration mixer W2 in a resin container V2 (Figures (a) and (b)), and then the remaining components (water s, zirconium acetate o, yttrium compound p, chelate compound q, catalyst r) are mixed in a glass container V1 using a magnetic stirrer W1 (Figures (c) and (d)). FIG. 3 shows an example of application in which the paint composition b2 is applied to a predetermined surface using an air spray X. In the following explanations of the examples and comparative examples, the reference numerals shown in the drawings have been omitted in order to clarify the names and amounts of each raw material.

[0074] 1. Example 1 9.86 g of a dilute acetic acid aqueous solution of zirconium acetate (57.4% content), 1.66 g of yttrium nitrate hexahydrate, 3.46 g of 2,4-pentanedione, 0.27 g of 60% nitric acid, and 30.55 g of 1-propanol 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.

[0075] Separately, the coating composition was sprayed onto a test piece as a control by air spraying, and then heat-treated at 80°C for 30 minutes to produce a coating film. This was then held at 1000°C for 60 minutes to produce a coating film. The coating film showed no damage such as cracks or peeling, and the film thickness was 1.5 μm. When the coating film 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 4. In addition, peaks of the underlying ceria were observed at 2θ values ​​of 29, 33, 48, 56, 59, 69, 77, and 79. The X-ray diffraction results of the examples are shown below in Figures 4 to 7. In Figures 4 to 7, "●" indicates the peak of yttria-stabilized zirconia.

[0076] 2. Example 2 5 g of yttria-stabilized zirconia (8YSZ) microparticles with an average particle size of 0.2 μm were weighed into a 200 ml resin container, and 95 g of 1-propanol was added. The mixture was stirred for 2 hours using a vibrating stirrer to prepare a 1-propanol dispersion of 8YSZ microparticles. 9.86 g of a dilute acetic acid aqueous solution of zirconium acetate (57.4% content), 1.66 g of yttrium nitrate hexahydrate, 3.46 g of 2,4-pentanedione, 0.27 g of 60% nitric acid, 5.65 g of the above-mentioned 1-propanol dispersion of yttria-stabilized zirconia (8YSZ) microparticles (5% by weight of zirconium acetate), and 24.9 g of 1-propanol were mixed into a 150 ml glass container and stirred for 3 hours using a magnetic stirrer to produce 50 g of a coating composition.

[0077] Separately, the coating composition was sprayed onto a test piece as a control by air spraying, and then heat-treated at 80°C for 30 minutes to produce a coating film. This was then held at 1000°C for 60 minutes to produce a coating film. The coating film showed no damage such as cracks or peeling, and the film thickness was 2.2 μm. When the coating film 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 5. In addition, peaks of the underlying ceria were observed at 2θ values ​​of 29, 33, 48, 56, 59, 69, 77, and 79.

[0078] 3. Example 3 10.11 g of a dilute acetic acid aqueous solution of zirconium acetate (57.4% content), 1.70 g of yttrium nitrate hexahydrate, 2.27 g of 3,5-heptanedione, 0.28 g of 60% nitric acid, and 31.33 g of 1-propanol 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.

[0079] Separately, the coating composition was applied to a test piece as a control by air spraying, and then heat-treated at 80°C for 30 minutes to produce a coating film. This was then held at 1000°C for 60 minutes to produce a coating film. The coating film showed no damage such as cracks or peeling, and the film thickness was 1.8 μm. When the coating film 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. In addition, peaks of the underlying ceria were observed at 2θ values ​​of 29, 33, 48, 56, 59, 69, 77, and 79.

[0080] 4. Example 4 5 g of yttria-stabilized zirconia (8YSZ) microparticles with an average particle size of 0.2 μm were weighed into a 200 ml resin container, and 95 g of 1-propanol was added. The mixture was stirred for 2 hours using a vibrating stirrer to prepare a 1-propanol dispersion of 8YSZ microparticles. 10.11 g of a dilute acetic acid aqueous solution of zirconium acetate (57.4% content), 1.70 g of yttrium nitrate hexahydrate, 2.27 g of 3,5-heptanedione, 0.28 g of 60% nitric acid, 5.79 g of the above-mentioned 1-propanol dispersion of yttria-stabilized zirconia (8YSZ) microparticles (5% by weight of zirconium acetate), and 25.54 g of 1-propanol were mixed into a 150 ml glass container and stirred for 3 hours using a magnetic stirrer to produce 50 g of a coating composition.

[0081] Separately, the coating composition was sprayed onto a test piece as a control by air spraying, and then heat-treated at 80°C for 30 minutes to produce a coating film. This was then held at 1000°C for 60 minutes to produce a coating film. The coating film showed no damage such as cracks or peeling, and the film thickness was 2.9 μm. When the coating film 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 7. In addition, peaks of the underlying ceria were observed at 2θ values ​​of 29, 33, 48, 56, 59, 69, 77, and 79.

[0082] 5. Comparative Example 1 (without chelating compound) 10.59 g of a dilute acetic acid aqueous solution of zirconium acetate (57.4% content), 1.78 g of yttrium nitrate hexahydrate, 0.29 g of 60% nitric acid, and 32.82 g of 1-propanol 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. No chelating agent was used as a chelating compound.

[0083] 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, resulting in cracks and peeling across the entire surface of the coating. Because peeling was observed in the coating when it was dried at 80°C, baking at 1000°C was not carried out.

[0084] In Comparative Example 1, since no chelate compound was added, the hydrolysis and polycondensation reaction of zirconium acetate proceeded too quickly, causing cracks on the front surface of the coating film, which then peeled off.

[0085] 6. Comparative Example 2 (without nitric acid) 9.91 g of a dilute acetic acid solution of zirconium acetate (57.4% content), 1.66 g of yttrium nitrate hexahydrate, 3.48 g of 2,4-pentanedione, and 30.72 g of 1-propanol were mixed in a 150 ml glass container and stirred for 3 hours using a magnetic stirrer to produce 50 g of coating composition. 60% nitric acid was not used as a catalyst.

[0086] Separately, the coating composition was sprayed onto a test piece as a control using an air spray and then heat-treated at 80°C for 30 minutes. As cracks occurred at the edge (periphery) of the coating film and peeling was observed, peeling was observed in the coating film when it was dried at 80°C, so baking at 1000°C was not carried out.

[0087] In Comparative Example 2, since nitric acid was not added as a catalyst, the hydrolysis and polycondensation reaction of zirconium acetate proceeded unevenly, which is thought to have caused cracks to form at the edges of the coating film, resulting in peeling.

[0088] Examples of combinations that can produce a suitable coating composition b2 and yttria-stabilized zirconia layer using a dilute acetic acid aqueous solution (containing water s) of zirconium acetate o, an yttrium compound p, a chelate compound q, a catalyst r, and an organic solvent t include the combinations described in Examples 1 to 4, as well as the following combinations. However, the present invention is not limited to these combinations. The combinations listed below can be selected regardless of whether the above-mentioned yttria-stabilized zirconia fine particles Pa are added or contained.

[0089] a) Dilute aqueous solution of zirconium acetate in acetic acid, yttrium(III) i-propoxide, 2,4-pentanedione, nitric acid, 1-propanol

[0090] b) Dilute aqueous solution of zirconium acetate in acetic acid, yttrium(III) i-propoxide, 3,5-heptanedione, nitric acid, 1-propanol

[0091] c) Zirconium acetate in dilute acetic acid, yttrium(III) i-propoxide, 2,4-pentanedione, nitric acid, 2-propanol

[0092] d) Zirconium acetate in dilute acetic acid, yttrium(III) i-propoxide, 3,5-heptanedione, nitric acid, 2-propanol

[0093] e) Dilute aqueous acetic acid solution of zirconium acetate, yttrium acetate, 2,4-pentanedione, acetic acid, 1-butanol

[0094] f) Dilute acetic acid solution of zirconium acetate, yttrium acetate, 3,5-heptanedione, acetic acid, 1-butanol

[0095] g) Dilute acetic acid solution of zirconium acetate, yttrium chloride, 2,4-pentanedione, hydrochloric acid, water, 1-propanol

[0096] h) Dilute acetic acid solution of zirconium acetate, yttrium chloride, 3,5-heptanedione, hydrochloric acid, 1-propanol

[0097] i) Dilute acetic acid solution of zirconium acetate, yttrium sulfate, 2,4-pentanedione, sulfuric acid, 1-propanol

[0098] j) Dilute acetic acid solution of zirconium acetate, yttrium sulfate, 3,5-heptanedione, sulfuric acid, 1-propanol

[0099] [Use of Yttria-Stabilized Zirconia Layer] Hereinafter, with reference to FIGS. 8 to 11, 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.

[0100] The electrochemical element E is used, for example, as a component of a solid oxide fuel cell that generates electricity when supplied with a fuel gas containing hydrogen and air. In the following description of the electrochemical element E, when describing the positional relationship of layers, the electrolyte layer 4 is used as the reference layer for describing 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. 8), 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. 8) may be referred to as the "front side," and the opposite side (lower side in FIG. 8) may be referred to as the "back side."

[0101] (electrochemical element) 8, 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.

[0102] 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.

[0103] (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 also have other shapes, such as a box shape, a cylinder shape, or a disk shape. The metal substrate 1 only needs to have sufficient strength 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.

[0104] The metal substrate 1 has a plurality of through-holes 1a extending from the front surface to the back surface. The through-holes 1a can be formed in the metal substrate 1 by, for example, mechanical, chemical, or optical drilling. The through-holes 1a allow gas to pass from the back surface to the front surface of the metal substrate 1. Porous metal can be used to make the metal substrate 1 gas-permeable. 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. 8 , a coating layer 1b may be formed on the outer surface of the metal substrate 1 (including the surface of the through-holes 1a). The coating layer 1b can be a metal oxide layer. For example, a Fe-Cr alloy can be coated with Co and then oxidized to form a metal oxide layer.

[0105] When an Fe-Cr alloy is used as the material for the metal substrate 1, this material has a thermal expansion coefficient similar 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.

[0106] (electrode layer) As shown in FIG. 8, the electrode layer 2 can be provided as a thin layer on the front surface of the metal substrate 1 in an area larger than the area where the through holes 1a are provided. When the electrode layer 2 is a thin layer, its thickness can be, for example, about 1 μm to 100 μm, preferably 5 μm to 50 μm. With such a thickness, it is 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 1a are provided is covered with the electrode layer 2. In other words, the through holes 1a 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 1a are provided facing the electrode layer 2.

[0107] Examples of materials that can be used for the electrode layer 2 include composites such as NiO-GDC, Ni-GDC, NiO-YSZ, Ni-YSZ, CuO-CeO, and Cu-CeO. In these examples, YSZ, GDC, and CeO can be referred to as aggregates of the composite. The electrode layer 2 is preferably formed by a low-temperature firing method (e.g., a wet method using a firing process at a low temperature without firing at a high temperature above 1100°C), a spray coating method (e.g., thermal spraying, aerosol deposition, aerosol gas deposition, powder jet deposition, particle jet deposition, cold spray, etc.), a PVD method (e.g., sputtering, pulsed laser deposition, etc.), or a CVD method. These processes, which can be used at low temperatures, can produce a good electrode layer 2 without firing at a high temperature above 1100°C. This is preferable because it prevents damage to the metal substrate 1 and suppresses interdiffusion of elements between the metal substrate 1 and the electrode layer 2, resulting in an electrochemical element with excellent durability. Furthermore, using a low-temperature firing method is even more preferable because it makes it easier to handle the raw materials.

[0108] 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. The electrode layer 2 is formed, for example, 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.

[0109] (middle class) As shown in FIG. 8, 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 a thin layer, its thickness can be, for example, about 1 μm to 100 μm, preferably about 2 μm to 50 μm, and more preferably about 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.

[0110] The intermediate layer 3 is preferably formed by a low-temperature firing method (e.g., a wet method using firing at a low temperature without firing at a high temperature 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 at low temperatures can provide the intermediate layer 3 without firing at a high temperature above 1100°C. This prevents interdiffusion of elements between the metal substrate 1 and the electrode layer 2 without damaging the metal substrate 1, resulting in an electrochemical element E with excellent durability. Furthermore, using a low-temperature firing method is more preferable because it facilitates handling of raw materials.

[0111] The intermediate layer 3 preferably has oxygen ion (oxide ion) conductivity. Furthermore, it is more preferable that the intermediate layer 3 has mixed conductivity of oxygen ions (oxide ions) and electrons. An intermediate layer 3 having these properties is suitable for application to the electrochemical element E.

[0112] (electrolyte layer) As shown in FIG. 8, 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. Alternatively, it may be formed as a thin film having 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 joining the electrolyte layer 4 to the metal substrate 1, the electrochemical element as a whole can have excellent robustness. The electrolyte layer 4 is provided on the front surface of the metal substrate 1 in an area larger than the area where the through-hole 1a is provided. In other words, the through-hole 1a is formed inside the area of ​​the metal substrate 1 where the electrolyte layer 4 is formed.

[0113] Furthermore, gas leakage from the electrode layer 2 and intermediate layer 3 can be suppressed around the electrolyte layer 4. Specifically, 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 1a during operation of the SOFC. 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.

[0114] 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 for a higher operating temperature of the SOFC using electrochemical element E compared to ceria-based ceramics. For example, when electrochemical element E is used in an SOFC, a material such as YSZ that can exhibit high electrolyte performance even at high temperatures above 650°C can be used for the electrolyte layer 4. A hydrocarbon-based raw fuel, such as city gas or LPG, can be used as the raw fuel, and the raw fuel can be converted into the SOFC anode gas by steam reforming or other methods. This allows for the construction of a highly efficient SOFC system using the heat generated in the SOFC cell stack to reform the raw fuel gas.

[0115] The electrolyte layer 4 is preferably formed by a low-temperature firing method (a wet method using a firing process at a low temperature without 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. It is also preferably formed by 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 a CVD method. These low-temperature film-forming processes can produce a dense electrolyte layer 4 with excellent airtightness and gas barrier properties without firing at a high temperature above 1100°C. This suppresses damage to the metal substrate 1 and also suppresses interdiffusion of elements between the metal substrate 1 and the electrode layer 2, resulting in an electrochemical element E with excellent performance and durability. In particular, low-temperature firing and spray coating methods are preferred because they allow for low-cost elements to be realized. Furthermore, low-temperature firing and spray coating methods are even more preferred because they make it easy to obtain a dense electrolyte layer 4 that is airtight and has high gas barrier properties at low temperatures.

[0116] The electrolyte layer 4 is densely configured to prevent gas leakage of anode gas and 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 is preferably 95% or more, and more preferably 98% or more. Furthermore, when the electrolyte layer 4 is configured as a multi-layer structure, it is preferable that at least a portion of the layers contains a layer (a dense electrolyte layer) with a density of 98% or more, and more preferably a layer (a dense electrolyte layer) with a density of 99% or more. If 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 is configured as a multi-layer structure.

[0117] (Reaction prevention layer) The reaction prevention layer 5 can be formed as a thin layer on the electrolyte layer 4. When the layer is thin, its thickness can be, for example, about 1 μm to 100 μm, preferably about 2 μm to 50 μm, and more preferably about 4 μm to 25 μm. Such a thickness reduces the amount of expensive reaction prevention layer material used, thereby reducing costs and 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 providing the reaction prevention layer 5 between the electrolyte layer 4 and the counter electrode layer 6, the reaction between the components of the counter electrode layer 6 and the electrolyte layer 4 is effectively suppressed, thereby improving the long-term stability of the performance of the electrochemical element E. The reaction prevention layer 5 is preferably formed using an appropriate method that allows it to be formed at a processing temperature of 1100°C or less, because this prevents damage to the metal substrate 1 and also suppresses interdiffusion of elements between the metal substrate 1 and the electrode layer 2, resulting in an electrochemical element E with excellent performance and durability. For example, a low-temperature firing method (e.g., a wet method using firing in a low-temperature range without firing in a high-temperature range exceeding 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. can be appropriately used. In particular, the low-temperature firing method and the spray coating method are preferred because they allow low-cost elements to be realized. Furthermore, the low-temperature firing method is even more preferred because it makes it easier to handle the raw materials.

[0118] (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, about 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 LSCF and LSM (lanthanum strontium manganate), ceria-based oxides, and mixtures thereof. It is particularly preferable that the counter electrode layer 6 contains 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.

[0119] 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 method can suppress damage to the metal substrate 1 and 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 without firing at a high temperature 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 used as appropriate. Low-temperature firing and spray coating methods are particularly preferred, as they allow for low-cost elements to be realized. Furthermore, low-temperature firing is even more preferred, as it facilitates handling of raw materials.

[0120] As described above, in the electrochemical element E according to the present invention, YSZ (yttria-stabilized zirconia) can be used for the electrolyte layer 4. Due to the advantage of obtaining an electrolyte layer 4 that is dense and has 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 be used as part of the electrode layer 2 or 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 obtained by curing the coating composition b2 of the present application can be used as part of this intermediate layer.

[0121] (Operates 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, oxygen O2 contained in the air is converted into electrons e in the counter electrode layer 6. - reacts with oxygen ions O 2- The oxygen ions O 2- The hydrogen H2 contained in the supplied fuel gas is converted into oxygen ions O2 in the electrode layer 2 (see FIG. 8). 2- This reacts with the cathode to produce water HO and electrons 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 solid oxide fuel cell, and the counter electrode layer 6 functions as the air electrode (cathode).

[0122] (Method of manufacturing an electrochemical element) Next, a method for manufacturing the electrochemical element E according to this embodiment will be described. In the following explanation, an example will be mainly described in which the coating composition b2 according to the present invention is used to form an yttria-stabilized zirconia layer on the electrode layer 2 and part of the intermediate layer 3, and further on the electrolyte layer 4.

[0123] (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 1a can be formed in predetermined positions of the plate by laser processing or the like. Alternatively, the 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 1b (coating layer) in the electrode layer formation step described below.

[0124] (Electrode layer formation step) In the electrode layer forming step, an electrode layer 2 is formed in a thin film state on an area of ​​the front surface of the metal substrate 1 obtained in the metal substrate preparation step that is larger than the area where the through-holes 1a are formed. The through-holes 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, or the like), a PVD method (sputtering, pulsed laser deposition, or the like), or the like. Whichever 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.

[0125] When the electrode layer formation step is performed by a low-temperature firing method, specifically, a material powder and a solvent (dispersion medium) are mixed to prepare 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). The electrode layer 2 can be compression molded by, for example, CIP (Cold Isostatic Pressing), roll pressing, or RIP (Rubber Isostatic Pressing). The electrode layer 2 is preferably fired at a temperature of 800°C or more and 1100°C or less. The order of the electrode layer smoothing step and the electrode layer firing step can also be reversed.

[0126] In addition, when forming an electrochemical element having an intermediate layer 3, the electrode layer smoothing step and the electrode layer firing step can be omitted, or the electrode layer smoothing step and the electrode layer firing step can be included in the intermediate layer smoothing step and the intermediate layer firing step described below. The electrode layer smoothing step can also be carried out by lapping, leveling, cutting and polishing the surface, or the like.

[0127] (Diffusion suppression 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 results in 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 the Co. Alternatively, 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 the Co.

[0128] In either case, it is desirable to carry out the treatment at a temperature of 1100°C or less, which can prevent damage to the metal substrate 1. Furthermore, a metal oxide layer 1b (diffusion-inhibiting layer) may be formed on the surface of the metal substrate 1 during the firing process in the intermediate layer formation step, which will be described later.

[0129] (Intermediate layer formation step) In the intermediate layer formation 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 at a low temperature of 1100°C or less), 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 to prevent deterioration of the metal substrate 1.

[0130] When the intermediate layer formation step is performed by a low-temperature firing method, the step is specifically performed as follows: First, a material powder for the intermediate layer 3 is mixed with a solvent (dispersion medium) to prepare a material paste, and the paste is applied to the front surface of the metal substrate 1. Suitable materials for the intermediate layer include ceria-based ceramics such as gadolinium-doped ceria (GDC), yttrium-doped ceria (YDC), and samarium-doped ceria (SDC). If the material paste contains the coating composition b2 according to the present invention, 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 lower (intermediate layer firing step). The intermediate layer 3 can be rolled by, for example, CIP (cold isostatic pressing), roll pressing, or RIP (rubber isostatic pressing). The intermediate layer is preferably fired at a temperature of 800°C or higher and 1100°C or lower. This is because such a temperature allows for the formation of a high-strength intermediate layer 3 while suppressing damage and deterioration of the metal substrate 1. The intermediate layer 3 is more preferably fired at 1050°C or lower, and even more preferably 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 carried out by lapping, leveling, cutting and polishing the surface, or the like.

[0131] (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, covering the electrode layer 2 and the intermediate layer 3. Alternatively, the electrolyte layer 4 may be formed as a thin film with 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). 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 the method used, it is preferable to perform the process at a temperature of 1100°C or less to prevent deterioration of the metal substrate 1.

[0132] To form a high-quality electrolyte layer 4 that is dense and has high airtightness and gas barrier properties at a temperature 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 air spraying or the like, and then baking at a temperature of 1100° C. or less.

[0133] (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 low-temperature firing, 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. Regardless of the method used, it is preferable to perform the process at a temperature of 1100°C or less to prevent deterioration of the metal substrate 1. In order to flatten the upper surface of the reaction prevention layer 5, for example, a leveling process or a cutting / polishing process may be performed after the formation of the reaction prevention layer 5, or a press process may be performed after wet formation and before firing.

[0134] (Counter electrode layer formation step) In the counter electrode layer formation step, the counter electrode layer 6 is formed as a thin layer 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 to suppress deterioration of the metal substrate 1.

[0135] In this manner, it is possible to manufacture the electrochemical element E. Note that, 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.

[0136] The electrochemical element E may be configured without either or both of the intermediate layer 3 and the reaction prevention layer 5. That is, the electrode layer 2 may be formed in contact with the electrolyte layer 4, or the electrolyte layer 4 may be formed in contact with the counter electrode layer 6. In this case, the intermediate layer forming step and the reaction prevention layer forming step are omitted from the above-described manufacturing method.

[0137] [Electrochemical elements, electrochemical modules, electrochemical equipment] 9 and 10, an example of a solid oxide fuel cell will be described with respect to an electrochemical element E, an electrochemical module M, an electrochemical device Y, and an energy system Z. As shown in Fig. 9, in this form of electrochemical element E, 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 FIG. 9, a plurality of electrochemical elements E are stacked with current collecting members 26 sandwiched therebetween to form an electrochemical module M. Here, stacking is an example of assembly. The current collecting members 26 are joined to the counter electrode layers 6 of the electrochemical elements E and the U-shaped members 7, electrically connecting them. Therefore, the electrochemical module M is electrically connected together in the stacking direction. The current collecting members 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 alloy members described above are used.

[0138] As shown in Fig. 10, the electrochemical module M has a gas manifold 17, a terminal member m1, and a current drawing portion m2. In the electrochemical element E, which is stacked with a current collecting member 26 sandwiched therebetween as shown in Fig. 9, 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 is supplied to the electrode layer 2 through the through-holes 1a of the metal substrate 1.

[0139] FIG. 10 shows an overview of the energy system Z and the electrochemical device Y. The energy system Z has 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 having a desulfurizer 31 and a reformer 34 and supplying 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 fuel cell that generates electricity when supplied with fuel.

[0140] 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.

[0141] 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 the 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, generating a reformed gas containing hydrogen.

[0142] The electrochemical module M generates electricity by electrochemical reaction using the reformed gas supplied from the reformer 34 and the 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.

[0143] 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 being electrically connected to each other, and one end (lower end) of each electrochemical element E is fixed to the gas manifold 17. The electrochemical element E generates electricity by causing an electrochemical reaction between the reformed gas supplied through the gas manifold 17 and air supplied from the blower 35.

[0144] 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.

[0145] 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 the 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.

[0146] 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.

[0147] 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 the reducing gas 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.

[0148] The reformed gas supplied to the gas manifold 17 is distributed to the 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 circulates 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.

[0149] 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 the 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.

[0150] 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. In other words, the heat exchanger 53 operates as a waste heat utilization section that reuses the heat discharged from the electrochemical device Y.

[0151] 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 combustion) 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 to utilize heat through combustion or to generate electricity using a fuel cell or the like, thereby making effective use of energy.

[0152] Alternative Embodiments of Electrochemical Modules FIG. 11 shows another embodiment of the electrochemical module M. The electrochemical module M according to this alternative embodiment is constructed by stacking the above-described electrochemical elements E with inter-cell connection members 71 sandwiched therebetween.

[0153] 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.

[0154] 11 , 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 from the back side of the electrochemical element E, i.e., the back surface of the metal substrate 1, to the electrode layer 2 through the through-holes 1a.

[0155] 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 in the electrochemical element E as a fuel cell, generating an electromotive force and current. The generated power is extracted from the electrochemical module M through the inter-cell connection members 71 at both ends of the stacked electrochemical elements E.

[0156] In this embodiment, the grooves 72 are formed on the front and back surfaces of the inter-cell connection member 71 so as to be perpendicular to each other, but the grooves 72 may also be formed on the front and back surfaces of the inter-cell connection member 71 so as to be parallel to each other.

[0157] [Another embodiment] (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, an oxygen sensor using a solid oxide, or the like. 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 described, in this example, the electrochemical device Y according to the present invention is configured 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 gases and electricity. That is, by supplying water HO and carbon dioxide CO to the electrolysis reaction section 10, they are decomposed to obtain hydrogen H and carbon monoxide CO as raw materials for synthesizing hydrocarbons. Then, hydrocarbons can be obtained in the hydrocarbon synthesis reaction section 30.

[0158] FIG. 12 is a system diagram showing the overall configuration of the hydrocarbon production system 100, and FIG. 13 shows an example of the configuration of an electrolysis cell unit U that constitutes the hydrocarbon production system 100.

[0159] As can be seen from Fig. 12, the hydrocarbon production system 100 is configured to include, in order, 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 an H2O separation section), and a carbon dioxide separation section 90 (illustrated as a CO2 separation section). In Fig. 12, the electrolysis reaction section 10, the first catalytic reaction section 20, and the second catalytic reaction section 30 are depicted separately, but as shown in Fig. 13, these sections 10, 20, and 30 can be provided as a single electrolysis cell unit U.

[0160] The electrolysis reaction section 10 electrolyzes at least a portion of the inflowing gas, the first catalytic reaction section 20 is a reverse water-gas shift reaction section that performs a reverse water-gas shift reaction on at least a portion of the inflowing gas, and the second catalytic reaction section 30 is a hydrocarbon synthesis reaction section that synthesizes at least a portion of the inflowing gas into hydrocarbons. The hydrocarbons synthesized here are mainly CH4 (hydrocarbons with one carbon atom), but may also include lower saturated hydrocarbons with two to four carbon atoms. In addition, hydrocarbons with a carbon number greater than 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 discharged from the second catalytic reaction section 30 is cooled.

[0161] The water separation unit 80 and the carbon dioxide separation unit 90 are units that remove at least a portion of predetermined components (H2O and CO2, in that order) from the gas flowing inside. The components removed and recovered by these units are returned to predetermined parts of the system via a water return path 81 and a carbon dioxide return path 91, as shown in the figure, and are reused. The H2O and CO2 returned via these return paths 81 and 91 are shown above the two return paths. As a result, this hydrocarbon production system 100 is established as a carbon-closed system that does not substantially release CO2 outside the system.

[0162] In the figure, the gases flowing into each part are shown before each part, and the gases released from each part are shown after each part.

[0163] In the electrolysis reaction section 10, H2O and CO2 as raw material gases are flowed in and electrolyzed inside, whereby H2O is decomposed into H2 and O2, and part of the CO2 is decomposed into CO and O2 and released.

[0164] The reaction is described as follows: 2H2O→2H2+O2 (formula 1) 2CO2→2CO+O2 (formula 2) These formulas 1 and 2 are also shown in the box representing the electrolytic reaction section 10 in FIG.

[0165] At least H2 and CO2 are introduced into the first catalytic reaction section 20 (reverse water-gas shift reaction section), where the reverse water-gas shift reaction occurs, converting CO2 into CO and H2 into H2O, which are then released.

[0166] The reaction is written 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 (CO2 and H2 react to produce CO and HO). CO2+H2⇔CO+H2O (Formula 3) This formula 3 is also shown in the box representing the first catalytic reaction section 20 (reverse water gas shift reaction section) in Figure 12. The reverse water gas shift catalyst cat1 used in the reaction is also shown schematically in the box. As this type of reverse water gas shift catalyst cat1, the inventors believe that a catalyst in which either nickel or iron, or both, is supported as a catalytically active component ca1 (metal catalyst) on one or more supports cb1 (metal oxide supports) selected from ceria-based metal oxides, zirconia-based metal oxides, and alumina-based metal oxides is preferable.

[0167] In the second catalytic reaction section 30 (hydrocarbon synthesis reaction section), at least H2 and CO are flowed in, and hydrocarbons are synthesized by a catalytic reaction. For example, the reaction in which CH4 is synthesized from CO and H2 is described as the following equilibrium reaction, but the reaction in which CH4 is synthesized from CO and H2 is a reaction in which the reaction described in the following formula 4 proceeds to the right (a reaction in which CO and H2 react to produce CH4 and HO). CO+3H2⇔CH4+H2O (Formula 4) This formula 4 is also shown in the box representing the second catalytic reaction section 30 (hydrocarbon synthesis reaction section) in Fig. 12. The hydrocarbon synthesis catalyst cat2 used in the reaction is also shown schematically in the box. As this type of hydrocarbon synthesis catalyst cat2, the inventors believe that 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, is preferable. Furthermore, the equilibrium reaction of (Equation 3) also occurs at this site. Furthermore, 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, and therefore it is also possible to synthesize hydrocarbons such as ethane and propane from CO and H2.

[0168] The H2O produced in the water separation section 80 is separated and returned to the upstream side of the electrolysis reaction section 10 via a water return line 81 (water recycle line).

[0169] The CO2 produced in the carbon dioxide separation section 90 is separated and returned to the upstream side of the electrolysis reaction section 10 via a carbon dioxide return path 91 (carbon dioxide recycle line).

[0170] As a result, in this hydrocarbon production system 100, hydrocarbons are ultimately synthesized and can be supplied to the outside.

[0171] An electrolysis cell unit U having such an electrochemical element E in an electrolysis 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 Fig. 13. Fig. 13 is a diagram illustrating the electrolysis cell unit U, including the direction of gas advection. In this figure, in order to clarify the electrochemical reaction system, the intermediate layer 3 and the reaction prevention layer 5 of the electrochemical element E in Figure 8 are omitted. Furthermore, in comparison with Figure 12, the heavy hydrocarbon separation section 70, the water separation section 80, and the carbon dioxide separation section 90 are omitted.

[0172] 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 channel forming member, and a current collecting member 26 serving as a supply channel component, and is configured to form an electrode layer side gas supply channel 7a and a counter electrode layer side gas supply channel 26a. H2O and CO2, which are the targets of electrolysis, are supplied to the electrode layer side gas supply channel 7a. Meanwhile, air g2 (O2), an example of an oxygen-containing gas, is supplied to the counter electrode layer side gas supply channel 26a. An electrochemical module M can be constructed by stacking (assembling) these electrolysis cell units U in the thickness direction of the unit, which is the left-right direction in FIG. 13. As described above, the electrolyte layer 4 and, as a part thereof, the electrode layer 2 can be constructed using the coating composition b2 according to the present invention.

[0173] This configuration of another embodiment is an example in which the electrochemical element E is used as the electrolytic reaction section 10, and as can be seen from FIG. 13, DC power is supplied between the electrode layer 2 and the counter electrode layer 6. In the illustrated example, power obtained from an AC power source 37 is converted to AC / DC by an inverter 38 and supplied to an electrochemical element E. Therefore, this inverter 38 serves as a power converter that distributes power to the electrochemical element E or, when these elements are integrated, to the electrochemical module M that is the assembly of these elements.

[0174] However, 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 to the surface on which the electrode layer 2 is formed, and the surfaces of the plurality of through holes 1a) is coated with a reverse water gas shift catalyst cat1. This coating layer 20b is indicated by a thick solid line. Furthermore, the electrode layer side gas supply path 7a is extended beyond the electrolysis reaction section 10, and the coating layer 20b is also provided on this extension side. Further beyond that, a hydrocarbon synthesis catalyst cat2 is applied to provide a coating layer 30b, which serves as a hydrocarbon synthesis reaction section 30.

[0175] As a result, in this configuration, the hydrocarbon synthesis reaction section 30 serves as a power converter that distributes power to the electrochemical elements E or, when these are integrated, to the electrochemical module M that is an assembly of these elements. Then, the gases obtained in the electrolysis reactor 10 and the reverse water gas shift reactor 20 can be used to obtain hydrocarbons in the hydrocarbon synthesis reactor 30 .

[0176] (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.

[0177] (3) In the above embodiment, the electrode layer 2 is made of a composite material such as NiO-GDC, Ni-GDC, NiO-YSZ, Ni-YSZ, CuO-CeO, or Cu-CeO, and the counter electrode layer 6 is made of a composite oxide such as LSCF or LSM. 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 serve as a fuel electrode and air to the counter electrode layer 6 to serve as an air electrode. This configuration can also be modified to configure the electrochemical element E so that the electrode layer 2 serves as an air electrode and the counter electrode layer 6 serves as a fuel electrode. That is, the electrode layer 2 is made of a composite oxide such as LSCF or LSM, and the counter electrode layer 6 is made of a composite material such as NiO-GDC, Ni-GDC, NiO-YSZ, Ni-YSZ, CuO-CeO, or Cu-CeO. In the electrochemical element E configured in this manner, air can be supplied to the electrode layer 2 to make it an air electrode, and hydrogen gas can be supplied to the counter electrode layer 6 to make it a fuel electrode, and the electrochemical element E can be used as a solid oxide fuel cell.

[0178] (4) In the above embodiment, an example was shown in which a composite oxide coating containing Co is formed on the surface of the Fe-Cr alloy of the metal substrate 1 to suppress the volatilization of Cr and other elements from this material. However, one or more of the U-shaped member 7 as a separator, the gas manifold 17, the current collecting member 26, and the inter-cell connecting member 71 as an interconnector may also be made of this type of alloy member.

[0179] On the other hand, as this type of oxide film, an oxide film of only Co may be formed on the surface of an Fe-Cr alloy, which is effective against volatilization of Cr.

[0180] The configurations disclosed in the above embodiments can be applied in combination with the 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. [Explanation of symbols]

[0181] 1. Metal substrate (metal support) 1a Through hole 2 electrode layer 3. Middle class 4 Electrolyte layer 5. Reaction prevention layer 6 Counter electrode layer 7 U-shaped member (separator) 10 Electrolytic 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 Reformed water tank 33 Vaporizer 34 Reformer (fuel converter) 35 Blower 36 Combustion section 38 Inverter (power converter) 39 Control Unit 40 Storage Container 41 Booster pump 42 Raw fuel supply route 43 Reformed water pump 44 Reformed water supply channel 45 Steam-containing raw fuel supply line 46 Reformed gas supply line 50 Combustion exhaust gas outlet 51 Combustion catalyst section 52 Combustion exhaust gas exhaust channel 53 Heat exchanger (exhaust heat utilization section) 70 Heavy Hydrocarbon Separation Section 71 Inter-cell connection material (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 Electrochemistry Module Pa Yttria-stabilized zirconia fine particles U Electrolysis Cell Unit Y Electrochemical Device Z Energy System o Zirconium acetate p Yttrium compounds q Chelate compounds r catalyst s water t Organic solvent

Claims

1. A method for producing an yttria-stabilized zirconia layer, comprising: mixing compositions containing zirconium acetate, an yttrium compound, a chelate compound, a catalyst, water, and an organic solvent as raw materials; applying the coating composition to the surface of an object and curing it to form an yttria-stabilized zirconia layer on the surface of the object; and curing the coating composition, wherein the coating composition has a zirconium acetate content of 10 to 30 mass%, a yttrium compound content of 1 to 10 mass%, a chelate compound content of 3 to 10 mass%, a catalyst content of 0.1 to 2 mass%, a water content of 5 to 15 mass%, and the organic solvent content being the remainder.

2. 2. The method for producing a yttria-stabilized zirconia layer according to claim 1, 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.

3. 3. The method for producing an yttria-stabilized zirconia layer according to claim 1, wherein the chelate compound is represented by the general formula (1). R1-CO-CH ２ -CO-R2 General formula (1) [In the formula, R1 and R2 are alkyl groups having 1 to 6 carbon atoms (including fluorinated alkyl groups), 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.]

4. The method for producing an yttria-stabilized zirconia layer according to any one of claims 1 to 3, wherein 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.

5. 5. The method for producing an yttria-stabilized zirconia layer according to claim 1, wherein the catalyst is at least one of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, carbonic acid, and acetic acid.

6. 6. The method for producing an yttria-stabilized zirconia layer according to claim 1, 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.

7. A method for producing an electrochemical device comprising the yttria-stabilized zirconia layer produced by the method for producing an yttria-stabilized zirconia layer according to any one of claims 1 to 6.

8. 8. The method for producing an electrochemical device according to claim 7, wherein the yttria-stabilized zirconia layer is provided on a metal support as an electrode layer.

9. A method for producing a solid oxide fuel cell, comprising producing a solid oxide fuel cell in which a power generating reaction occurs as an electrochemical element produced by the method for producing an electrochemical element according to claim 7 or 8.

10. A method for producing a solid oxide electrolysis cell, comprising producing a solid oxide electrolysis cell in which an electrolytic reaction occurs as an electrochemical element produced by the method for producing an electrochemical element according to claim 7 or 8.

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