Proton-conductive composite oxide powder and method for producing same

Abstract

A proton-conductive composite oxide powder according to the present invention contains 60 vol% or more of a composite oxide represented by BaScxM1-xO3-δ, and has an average particle diameter of 0.05 μm or less. A method for producing a proton-conductive composite oxide powder according to the present invention comprises: a precipitation step for adding, to an alkaline aqueous solution, at least one aqueous solution of a hydrochloric acid-based aqueous solution and a nitric acid-based aqueous solution which contain Ba ions, Sc ions, and ions of an M element (M is at least one element selected from Mo and W) and have a pH of less than 2, and adjusting the pH of the alkaline aqueous solution to 10 or more to less than 14 to obtain a precipitate, or a precipitation step for adding, to an alkaline aqueous solution containing ions of an M element (M is at least one element selected from Mo and W), at least one aqueous solution of a hydrochloric acid-based aqueous solution and a nitric acid-based aqueous solution which contain Ba ions and Sc ions and have a pH of less than 2, and adjusting the pH of the alkaline aqueous solution to 10 or more to less than 14 to obtain a precipitate; a drying step for drying the precipitate at a prescribed temperature to obtain a precursor powder; and a sintering step for sintering the precursor powder at a temperature of 700°C or higher. With the present invention, it is possible to provide a proton-conductive composite oxide powder which has a fine particle size that is suitable for producing an electrolyte membrane, and has a high content of BaSc0.8Mo0.2O3-δ, and a method for producing said proton-conductive composite oxide powder.

Description

Proton-conductive composite oxide powder and method for producing the same

[0001] The present invention relates to a proton-conductive composite oxide powder used for a proton-conductive solid electrolyte such as a fuel cell or a sensor, and a method for producing the same.

[0002] Various fuel cells are positioned as the core of technologies for realizing a decarbonized society. As materials for electrolyte membranes constituting fuel cells, proton-conductive composite oxides and ion-conductive composite oxides that are metal oxides are known. For example, Non-Patent Document 1 shows that a dense film made of a highly ion- or proton-conductive composite oxide can be utilized as an electrolyte of a fuel cell.

[0003] Conventionally known ion conductors include, for example, yttria-stabilized zirconia (ZrO ２ -Y ２ O ３ ). An electrolyte membrane made using yttria-stabilized zirconia has been commercialized as a member constituting a solid oxide fuel cell (hereinafter referred to as SOFC).

[0004] On the other hand, as proton-conductive composite oxides, for example, BaZr ０．８ Y ０．２ O ３－δ is known. A fuel cell using a proton-conductive composite oxide (hereinafter referred to as PCFC) has a structural feature that water vapor is exhausted on the air electrode side, and thus it is possible to improve the use efficiency of fuel gas. In addition, since PCFC is expected to achieve high power generation efficiency in a lower temperature range than SOFC, early social implementation of PCFC is expected.

[0005] However, Non-Patent Document 2 shows that the proton conductivity of conventionally known proton-conductive composite oxides significantly decreases in the intermediate temperature range of 300°C to 500°C. Therefore, the realization of a proton-conductive electrolyte membrane that can exhibit high proton conductivity in the intermediate temperature range is desired.

[0006] Patent Document 1 discloses a chemical formula BaSc ０．８ Mo ０．２ O ３－δIt has been shown that the composite oxide represented by BaSc exhibits extremely high proton conductivity in the medium temperature range. ０．８ Mo ０．２ O ３－δ Electrolyte membranes fabricated using composite oxides are considered suitable for fuel cells that have high-efficiency power generation capabilities in the medium temperature range.

[0007] On the other hand, producing high-quality electrolyte membranes requires the complex oxide to be in powder form. Furthermore, raw material powders suitable for electrolyte membrane production must have few impurities in the complex oxide and a fine particle size.

[0008] Generally, solid-phase reaction methods and liquid-phase synthesis methods such as coprecipitation are known as methods for producing complex oxides. When using solid-phase reaction methods, a grinding process is necessary to refine the powder particle size. The powder obtained by solid-phase reaction methods is ground using grinding techniques such as the ball mill method and the jet mill method, as described in Non-Patent Documents 3 and 4, for example.

[0009] International Publication No. 2024 / 053651

[0010] ENGINEERING JOURNAL: VOLUME 13 ISSUE 1 ISSN 0125-8281Nature Communications (2023) 14:7466 Powder Industry Research Society Vol. 30 No. 8 (1993) Powder Industry Research Society Vol. 6 No. 6 (1969)

[0011] However, since high grinding energy leads to the incorporation of impurities into the material being ground, it is difficult to achieve both low impurity levels and fine particle size at a high level using grinding methods such as those described in Non-Patent Documents 3 and 4.

[0012] In contrast, liquid-phase synthesis methods such as the coprecipitation method have the advantage of being able to obtain composite oxides with fine particle size without going through a grinding process. However, the BaSc described in Patent Document 1 ０．８ Mo ０．２ O ３－δ The component Ba has high hydration properties, and the pH at which it precipitates is extremely low compared to rare earth elements. As a result, Ba segregates and forms impurities, and single-phase BaSc is obtained by coprecipitation.０．８ Mo ０．２ O ３－δ It is difficult to obtain.

[0013] The present invention has been made in view of the problems of the prior art described above, and has a fine particle size suitable for the production of electrolyte membranes, and / or BaSc ０．８ Mo ０．２ O ３－δ The objective is to provide proton-conducting composite oxide powders with a high content of [substance name] and methods for producing them.

[0014] The inventors, after diligent research to achieve the above objective, have found that by drying the precipitate obtained by the precipitation method, BaSc ０．８ Mo ０．２ O ３－δ A precursor powder is prepared, and by calcining the precursor powder, a powder with a fine particle size suitable for electrolyte membrane fabrication and BaSc is produced. ０．８ Mo ０．２ O ３－δ We discovered that it is possible to obtain a proton-conducting composite oxide powder with a high content of [substance name], and thus completed the present invention.

[0015] The present invention provides the following proton-conducting composite oxide powder and a method for producing the same: [1] A proton-conducting composite oxide powder containing 60% by volume or more of a composite oxide represented by the following compositional formula (1), and having an average particle size of 0.05 μm or less. BaSc ｘ M １－ｘ O ３－δ (1) Here, M is one or more elements selected from Mo and W, x is between 0.6 and 0.9, and δ is between 0 and 2.0. [2] Specific surface area is 1.5 m² ２ / g or more 100.0m ２ A proton-conducting composite oxide powder as described in [1] above, wherein the amount is less than or equal to / g. [3] A proton-conducting composite oxide powder as described in [1] or [2] above, containing 90% by volume or more of a composite oxide represented by the following composition formula (1). BaSc ｘ M １－ｘ O ３－δ (1) Here, M is one or more elements selected from Mo and W, x is between 0.6 and 0.9, and δ is between 0 and 2.0. [4] Sc ２O ３ BaCO ３ A proton-conducting composite oxide powder according to any one of [1] to [3] above, wherein the total content of graphite is less than 5% by volume. [5] A method for producing a proton-conducting composite oxide powder, comprising: a precipitation step of adding at least one aqueous solution of a hydrochloric acid-based aqueous solution and a nitric acid-based aqueous solution having a pH of less than 2 and containing Ba ions, Sc ions and ions of element M (M is one or more elements selected from Mo and W) to an alkaline aqueous solution to adjust the pH of the alkaline aqueous solution to 10 or more and less than 14 to obtain a precipitate; a precipitation step of adding at least one aqueous solution of a hydrochloric acid-based aqueous solution and a nitric acid-based aqueous solution having a pH of less than 2 and containing Ba ions and Sc ions to an alkaline aqueous solution having a pH of less than 2 and adjusting the pH of the alkaline aqueous solution to 10 or more and less than 14 to obtain a precipitate; a drying step of drying the precipitate at a predetermined temperature to obtain a precursor powder; and a calcination step of calcining the precursor powder at a temperature of 700°C or higher. [6] The precursor powder is BaCO ３ or Ba(OH) ２ The method for producing proton-conducting composite oxide powder according to [5] above, further comprising a mixing step of mixing with the precursor powder and the BaCO ３ or Ba(OH) ２ The mixing ratio of the precursor powder and the BaCO2 is such that the mass ratio is 1:X (where X is less than 2.0). ３ or Ba(OH) ２ A method for producing proton-conducting composite oxide powder according to [6] above, comprising mixing the above, and the firing step comprising firing the mixture at a firing temperature of 800°C or more and 1500°C or less and a firing time of 1 hour or more.

[0016] According to the present invention, a fine particle size suitable for the production of an electrolyte membrane is obtained, and BaSc ０．８ Mo ０．２ O ３－δ This invention provides proton-conducting composite oxide powders with a high content of [substance name] and methods for producing them.

[0017] This is the X-ray diffraction pattern of the proton-conducting composite oxide powder obtained in Example 1. This is the X-ray diffraction pattern of the proton-conducting composite oxide powder obtained in Example 2. This is the X-ray diffraction pattern of the proton-conducting composite oxide powder obtained in Example 3. This is the X-ray diffraction pattern of the proton-conducting composite oxide powder obtained in Example 4. This is the X-ray diffraction pattern of the proton-conducting composite oxide powder obtained in Example 5. This is the X-ray diffraction pattern of the proton-conducting composite oxide powder obtained in Example 6. This is the X-ray diffraction pattern of the proton-conducting composite oxide powder obtained in Example 7. This is the X-ray diffraction pattern of the proton-conducting composite oxide powder obtained in Example 8. This is the X-ray diffraction pattern of the proton-conducting composite oxide powder obtained in Comparative Example 2. This is an SEM image of the proton-conducting composite oxide powder obtained under the conditions of Example 6. This is an SEM image of the proton-conducting composite oxide powder obtained under the conditions of Comparative Example 2.

[0018] The proton-conducting composite oxide powder of the present invention contains 60% by volume or more of the composite oxide represented by the following compositional formula (1): BaSc ｘ M １－ｘ O ３－δ (1) Here, M is one or more elements selected from Mo and W, x is between 0.6 and 0.9, and δ is between 0 and 2.0. Furthermore, the average particle size of the proton-conducting composite oxide powder of the present invention is 0.05 μm or less.

[0019] Furthermore, the composite oxide represented by the above compositional formula (1) contained in the proton-conducting composite oxide powder of the present invention belongs to the category of composite oxides represented by the following compositional formula (2). BaZ ｘ N １－ｘ O ３－δ (2) Here, Z is an element with an ionic radius of 0.52 to 0.97 Å, and N is an element other than Z whose ionic radius is 70 to 130% of the ionic radius of Z, or a mixed composition of multiple elements whose average ionic radius is 70 to 130% of the ionic radius of Z.

[0020] In composition formula (1), element M substitutes for a portion of Sc and is one or more elements selected from Mo and W. Furthermore, the Sc content ratio x is preferably 0.6 to 0.9, and more preferably 0.70 to 0.85. By setting it within this range, BaSc ｘ M １－ｘ O ３－δ The internal charge remains neutral, and the cubic perovskite structure becomes stable.

[0021] The oxygen content ratio δ in the above compositional formula is between 0 and 2.0. If the value of δ is greater than 2.0, BaSc ｘ M １－ｘ O ３－δ The charge inside is not kept neutral, and the cubic perovskite structure of the composite oxide represented by the above compositional formula (1) becomes unstable. From this viewpoint, it is preferable that the value of δ is 0.15 or more and 0.25 or less.

[0022] As described above, the average particle size of the proton-conducting composite oxide powder of the present invention is 0.05 μm or less, and the proton-conducting composite oxide powder of the present invention is a powder with fine particle size. If the average particle size of the proton-conducting composite oxide powder is larger than 0.05 μm, the composition inside the particles tends to become heterogeneous. From this viewpoint, the average particle size of the proton-conducting composite oxide powder of the present invention is preferably 0.04 μm or less, more preferably 0.03 μm or less, and even more preferably 0.02 μm or less. The lower limit of the average particle size of the proton-conducting composite oxide powder of the present invention is not particularly limited, but from the viewpoint of suppressing secondary aggregation of the proton-conducting composite oxide powder, it is usually, for example, 0.01 μm or more. Note that the average particle size of the proton-conducting composite oxide powder in the present invention is calculated from the full width at half maximum of XRD (X-ray diffraction). The measurement of the XRD full width at half maximum (FWHM) is not particularly limited, but for example, the XRD FWHM can be measured using an X-ray diffractometer (Panalytical Corporation, product name "Aeris"). Alternatively, the XRD FWHM can be measured under the conditions described in the examples.

[0023] The specific surface area of ​​the proton-conducting composite oxide powder of the present invention is 1.5 m². ２ / g or more 100.0m ２ It is preferable that it be less than or equal to 10 m ２ / g or more 100.0m ２ It is more preferable that the value be less than or equal to / g. Being within this range further suppresses the heterogeneity of the internal composition of the proton-conducting composite oxide powder particles, and also increases the powder packing density in the electrolyte membrane fabrication process, making it easier to obtain a dense electrolyte membrane. In this invention, specific surface area is defined by the BET method. While the measurement of specific surface area by the BET method is not particularly limited, for example, it can be measured using a specific surface area measuring device (MOUNTECH, product name "Macsorb HM model-1201").

[0024] Furthermore, as described above, the proton-conducting composite oxide powder of the present invention contains 60% by volume or more of the composite oxide represented by the above compositional formula (1), and contains a high proportion of the composite oxide represented by the above compositional formula (1). If the content of the composite oxide represented by the above compositional formula (1) is less than 60% by volume, the proton conductivity may decrease significantly. In addition, the content of the composite oxide represented by the above compositional formula (1) is preferably 90% by volume or more, and more preferably 95% by volume or more. There is no particular upper limit to the content of the composite oxide represented by the above compositional formula (1), and ideally it is 100% by volume. However, the proton-conducting composite oxide powder of the present invention may contain, for example, less than 5% by volume of impurities. Examples of impurities in this case include unreacted products such as Sc ２ O ３ BaCO ３ Examples include graphite. When the content of the above impurities in the proton-conducting composite oxide powder is low, it may be described as a proton-conducting composite oxide powder with high purity of the composite oxide represented by the above compositional formula (1). Furthermore, the content of the composite oxide represented by the above compositional formula (1) in the proton-conducting composite oxide powder can be estimated, for example, by the Rietveld method.

[0025] Next, the method for producing the proton-conducting composite oxide powder of the present invention will be described. The method for producing the proton-conducting composite oxide powder of the present invention includes a precipitation step in which at least one aqueous solution of a hydrochloric acid-based aqueous solution and a nitric acid-based aqueous solution having a pH of less than 2 and containing Ba ions, Sc ions, and ions of element M (M is Mo or W) is added to an alkaline aqueous solution to adjust the pH of the alkaline aqueous solution to 10 or more and less than 14 in order to obtain a precipitate; a precipitation step in which at least one aqueous solution of a hydrochloric acid-based aqueous solution and a nitric acid-based aqueous solution having a pH of less than 2 and containing Ba ions, Sc ions, and containing M ions, is added to an alkaline aqueous solution having ions of element M (M is one or more elements selected from Mo and W) to adjust the pH of the alkaline aqueous solution to 10 or more and less than 14 in order to obtain a precipitate; a drying step in which the precipitate is dried at a predetermined temperature to obtain a precursor powder; and a calcination step in which the precursor powder is calcined at a temperature of 800°C or higher. Each step will be described below.

[0026] (Precipitation Process) In the precipitation process, an aqueous solution containing all of Ba ions, Sc ions, and ions of element M (where M is Mo or W), or at least one aqueous solution of hydrochloric acid and nitric acid, with a pH of less than 2 and containing Ba ions and Sc ions, is added to an alkaline aqueous solution or an alkaline aqueous solution containing ions of element M to adjust the pH of the alkaline aqueous solution to 10 or more and less than 14 to obtain a precipitate. An aqueous solution containing Ba ions, Sc ions, and ions of element M (where M is Mo or W), with a pH of less than 2, is hereinafter referred to as the precursor aqueous solution. The precursor aqueous solution contains Ba ions, Sc ions, and ions of element M (where M is one or more elements selected from Mo or W). This precursor aqueous solution can also be obtained by dissolving water-soluble metal salts containing each metal element in water. The water-soluble metal salt is not particularly limited, but examples of water-soluble metal salts that can be selected include carbonates, chlorides, hydroxides, acetates, and citrates. Alternatively, for each metal element, a precursor aqueous solution may be prepared using two or more compounds selected from, for example, carbonates, chlorides, hydroxides, acetates, and citrates.

[0027] The metal content in the precursor aqueous solution is preferably more than 1% by mass and less than 20% by mass, and more preferably more than 3% by mass and 10% by mass or less, in terms of the final composite oxide. This range ensures that the reaction in the precursor aqueous solution proceeds homogeneously. As mentioned above, the metal content in the precursor aqueous solution is preferably prepared in a stoichiometric ratio that yields the final composite oxide; however, if there are elements lost during the process, this may be taken into consideration during preparation.

[0028] The pH of the above precursor aqueous solution is less than 2.0, and preferably less than 1.0. If the pH is 2.0 or higher, the Ba contained in the precursor aqueous solution will be Ba-Sc complex oxide or BaCO2. ３ This makes it easier to generate BaSc ｘ M １－ｘ O ３－δ The formation of the precursor aqueous solution is inhibited. The precursor aqueous solution is an aqueous solution of at least one of a hydrochloric acid-based aqueous solution and a nitric acid-based aqueous solution, and the concentrations of hydrochloric acid and nitric acid can be adjusted so that the pH is as described above.

[0029] The precursor aqueous solution obtained in this way is added to an alkaline aqueous solution or an alkaline aqueous solution containing ions of element M to adjust the pH to 10 or higher and less than 14, thereby obtaining a precipitate. The alkaline aqueous solution used is not particularly limited, but for example, an aqueous sodium hydroxide solution or ammonium hydroxide can be used. The concentration of the alkaline aqueous solution can be appropriately selected from the viewpoint of adjusting the pH to obtain a precipitate. The method of adding the precursor aqueous solution to the alkaline aqueous solution is not particularly limited, but typically a titration method is used. In this case, the titration rate of the precursor aqueous solution is preferably 0.01 ml / s to 10.0 ml / s, and more preferably 0.05 ml / s to 1.0 ml / s.

[0030] When the precursor aqueous solution is added to an alkaline aqueous solution or an alkaline aqueous solution containing ions of element M, it is preferable to maintain the aqueous solution at a predetermined temperature. While the specific conditions are not particularly limited, for example, a temperature of 60°C to 100°C is preferred, and 90°C to 100°C is more preferred. Within this range, precipitate formation can be achieved more effectively. The alkaline aqueous solution itself can also be heated to the same temperature as described above. This method helps to suppress temperature variations in the aqueous solution that occur when the precursor aqueous solution is added dropwise.

[0031] After separating the precipitate obtained as described above by filtration, it is preferable to wash it with water two or more times to remove by-products such as sodium chloride.

[0032] (Drying process) In the drying process, the precipitate is dried at a predetermined temperature to obtain a precursor powder. For example, the precipitate can be dried at a temperature of 120°C to 200°C for 1 to 12 hours to obtain the precursor powder.

[0033] (Castration Process) In the calcination process, the precursor powder is calcined at a temperature of 700°C or higher. By calcining the precursor powder, the formation of the composite oxide represented by the above composition formula (1) is promoted, and a proton-conducting composite oxide powder with a fine particle size can be produced. The calcination of the precursor powder is preferably carried out in air or in an inert gas, and more preferably in an inert gas. The calcination temperature is 700°C or higher as described above. Furthermore, the calcination temperature is preferably 800°C or higher, more preferably 800°C to 1500°C, and even more preferably 900°C to 1100°C. The calcination time is preferably 1 hour or more, more preferably 2 hours or more, even more preferably 2 hours to 50 hours, and even more preferably 5 hours to 10 hours. By calcining within this range, Sc ２ O ３The formation can be suppressed. The proton-conductive composite oxide powder thus obtained has a fine particle size and does not require fine grinding as compared with the powder obtained by solid-phase reaction synthesis. Further, by firing in an inert gas, the particle size of the obtained proton-conductive composite oxide powder tends to become fine.

[0034] (Mixing step) The method for producing a proton-conductive composite oxide powder of the present invention may further include a mixing step of mixing a precursor powder with BaCO ３ or Ba(OH) ２ to obtain a mixture. In this case, in the firing step, instead of the precursor powder, a mixture of the precursor powder and BaCO ３ is fired.

[0035] In the firing step, by mixing BaCO ３ or Ba(OH) ２ with the precursor powder and then performing firing, the purity of BaSc ｘ M １－ｘ O ３－δ in the proton-conductive composite oxide powder can be further improved. The mixing ratio is such that the weight of BaCO ３ or Ba(OH) ２ is less than 2.0 with respect to 1.0 of the weight of the proton-conductive composite oxide powder. It is preferable to mix the precursor powder with BaCO ３ or Ba(OH) ２ , more preferably to mix such that the mixing ratio is 0.2 or more and less than 2.0, and even more preferably to mix such that the mixing ratio is 0.5 or more and 1.5 or less. With such a mixing ratio, the formation of carbides derived from BaCO ３ and the formation of Sc ２ O ３ which inhibits the formation of BaSc ｘ M １－ｘ O ３－δ can be suppressed, and the purity of BaSc ｘ M １－ｘ O ３－δ can be further improved.

[0036] The precursor powder and BaCO ３ or Ba(OH) ２The method of mixing is not particularly limited and can be mixed by an appropriate method. Specifically, for example, a ball mill, a mortar, etc. can be applied. In the case of a ball mill, it is preferable to mix under conditions such as a rotation speed of 100 to 200 rpm and a mixing time of 5 to 30 minutes.

[0037] The precursor powder and BaCO ３ or Ba(OH) ２ As the firing conditions of the mixture obtained by mixing, 800°C or higher and 1500°C or lower are preferable, and 900°C or higher and 1400°C or lower are more preferable. Further, the firing time is preferably 1 hour or longer, more preferably 2 hours or longer, even more preferably 2 hours or longer and 50 hours or shorter, and still more preferably 5 hours or longer and 10 hours or shorter. By firing under such conditions, impurities contained in the precursor powder react, and the purity of BaSc ｘ M １－ｘ O ３－δ can be further improved. In addition, since the treatment can be performed at a lower temperature than the conventional solid-phase reaction synthesis, the process time can be shortened and the manufacturing cost can be reduced.

[0038] The proton-conductive composite oxide powder thus obtained has a very fine particle size compared to the conventional ones. Further, the proton-conductive composite oxide powder thus obtained has a higher content of the composite oxide represented by the above compositional formula (1) than the conventional ones. Therefore, the proton-conductive composite oxide powder of the present invention and the proton-conductive composite oxide powder produced by the manufacturing method of the proton-conductive composite oxide powder of the present invention are suitable for the electrolyte membrane used in PCFC.

[0039] Hereinafter, examples and comparative examples will be shown to explain the present invention in more detail, but the present invention is not limited to the following examples.

[0040] [Example 1] BaCl ２ ·2H ２ O, Sc ２ O ３ and MoO ３Aqueous solutions of Ba, Sc, and Mo were prepared by dissolving them in hydrochloric acid, respectively. These solutions were weighed and mixed so that the molar ratio of Ba:Sc:Mo was 1:0.8:0.2. At this time, the amount of BaSc in relation to the total aqueous solution was also measured. ０．８ M ０．２ O ３－δ A precursor aqueous solution was prepared by adjusting the conversion mass ratio to 2.6% by mass. The pH of this precursor aqueous solution was 0.3.

[0041] The obtained precursor aqueous solution was added dropwise at a rate of 0.09 ml / s to a 10 mol / L sodium hydroxide aqueous solution heated to 90°C, adjusting the pH of the aqueous solution to between 10 and 14, and then maintained at 90°C for 30 minutes.

[0042] A precipitate formed, and the resulting precipitate was filtered and washed twice with water. The washed precipitate was dried at 120°C for 12 hours to obtain a precursor powder.

[0043] The obtained precursor powder was crushed in a mortar and then calcined at a calcination temperature of 800°C for 2 hours under an atmospheric environment to obtain a proton-conducting composite oxide powder.

[0044] [Example 2] A proton-conducting composite oxide powder was obtained in the same manner as in Example 1, except that the firing temperature was 1000°C.

[0045] [Example 3] A proton-conducting composite oxide powder was obtained in the same manner as in Example 1, except that the firing temperature was 1200°C.

[0046] [Example 4] Precursor powder and BaCO3 ３ The mixing ratio of the precursor powder to the BaCO2 is such that the mass ratio is 1:0.5. ３ A proton-conducting composite oxide powder was obtained in the same manner as in Example 1, except that the mixture was added, mixed in a ball mill at 200 rpm for 10 minutes, and then calcined at 1000°C for 2 hours.

[0047] [Example 5] Precursor powder and BaCO3 ３ The mixing ratio of the precursor powder to the BaCO3 is 1:1 by mass. ３A proton-conducting composite oxide powder was obtained in the same manner as in Example 4, except that a certain substance was added.

[0048] [Example 6] A proton-conducting composite oxide powder was obtained in the same manner as in Example 5, except that the powder was fired at a firing temperature of 1000°C for 10 hours.

[0049] [Example 7] A proton-conducting composite oxide powder was obtained in the same manner as in Example 6, except that the powder was fired in a nitrogen atmosphere at a firing temperature of 1000°C for 10 hours.

[0050] [Example 8] BaNO ３ Dissolve in water to prepare a barium nitrate aqueous solution, and also, Sc ２ O ３ A nitrate Sc aqueous solution was prepared by reacting with nitric acid. The prepared nitrate Ba aqueous solution and nitrate Sc aqueous solution were weighed so that the molar ratio of Ba:Sc was 1:0.8, and mixed to prepare the aqueous solution to be dropped. Meanwhile, the molar ratio of Mo to Ba in the aqueous solution to be dropped was 1:0.2 (NH ４ ) 6Mo ７ O ２４ 4H ２ O was dissolved in a 10 mol / L sodium hydroxide solution to prepare a dropwise aqueous solution. The pH of the precursor aqueous solution at this time was 1.3.

[0051] The target aqueous solution was added dropwise to the target aqueous solution heated to 90°C at a dropping rate of 0.09 ml / s, adjusting the pH of the aqueous solution to be between 10 and 14, and then maintained at 90°C for 30 minutes.

[0052] A precipitate formed, and the resulting precipitate was filtered and washed twice with water. The washed precipitate was dried at 120°C for 12 hours to obtain a precursor powder.

[0053] After crushing the obtained precursor powder in a mortar, add Ba(OH)2 of the same weight as the precursor powder. ２ The mixture was mixed with the other ingredients, and the resulting mixed powder was fired at a firing temperature of 1400°C in an air atmosphere for 10 hours to obtain a proton-conducting composite oxide powder.

[0054] [Comparative Example 1] A proton-conducting composite oxide powder was obtained in the same manner as in Example 1, except that the firing temperature was 600°C.

[0055] [Comparative Example 2] BaCO ３ and Sc ２ O ３ , and MoO ３ The powder reagents were weighed in a molar ratio of 1:0.8:0.2, mixed using a ball mill for 60 minutes, and the resulting powder mixture was subjected to a heat treatment at 900°C for 12 hours.

[0056] The powder mixture after calcination heat treatment was filled into a mold and a pressure of 100 MPa was applied to form a molded body. The resulting molded body was then subjected to heat treatment at 1500°C for 12 hours to obtain a sintered body of a proton-conducting composite oxide.

[0057] The obtained sintered proton-conducting composite oxide was processed into granules with a particle size of 1 mm or less using a mortar and pestle.

[0058] A granular proton-conducting composite oxide was ground into a powder using a wet bead mill with 3 mm particle size zirconia beads and ethanol for 1 hour.

[0059] The obtained proton-conducting composite oxide powder was further pulverized for 1 hour using a wet bead mill with 1 mm particle size zirconia beads and ethanol to obtain a proton-conducting composite oxide powder with a fine particle size.

[0060] Table 1 shows the evaluation results of the proton-conducting composite oxide powders obtained in the examples and comparative examples. The evaluation of each item was performed as follows: <BaSc ｘ Mo １－ｘ O ３－δ Purity > The obtained proton-conducting composite oxide powder was subjected to XRD measurement (2θ / θ method, Cu Kα, 40kV / 40mA), and analysis by the Rietveld method was performed to determine the amount of BaScxMo contained. １－ｘ O ３－δ Estimate the volume percentage of the composite oxide (δ is between 0 and 2.0), and then calculate BaSc ｘ Mo １－ｘ O ３－δ The purity was set to (δ between 0 and 2.0).

[0061] <Average particle size of proton-conducting composite oxide powder> The average particle size of the proton-conducting composite oxide powder was calculated from the full width at half maximum (FWHM) of the XRD. An X-ray diffractometer (Panalytical, product name "Aeris") was used for the measurement. <Specific surface area> The specific surface area of ​​the proton-conducting composite oxide powder was obtained from the gas adsorption isotherm using the BET theory (multilayer adsorption theory). A specific surface area analyzer (MOUNTECH, product name "Macsorb HM model-1201") was used for the measurement.

[0062] Table 1 shows the evaluation results of the proton-conducting composite oxide powders of Examples 1-8 and Comparative Examples 1-2. Figures 1-9 show the X-ray diffraction patterns of the proton-conducting composite oxide powders of Examples 1-8 and Comparative Example 2, respectively. Furthermore, Figure 10 shows the SEM image of the proton-conducting composite oxide powder of Example 6, and Figure 11 shows the SEM image of the proton-conducting composite oxide powder of Comparative Example 2.

[0063]

[0064] In Examples 1 to 3, proton-conducting composite oxide powders with very fine particle sizes were obtained. In Examples 4 to 8, BaCO3 was obtained. ３ or Ba(OH) ２ By mixing and calcining the materials, a proton-conducting composite oxide powder with even higher purity was obtained.

Claims

A proton-conducting composite oxide powder containing 60% by volume or more of a composite oxide represented by the following compositional formula (1), and having an average particle size of 0.05 μm or less. BaSc ｘ M １－ｘ O ３－δ (1) Here, M is one or more elements selected from Mo and W, x is between 0.6 and 0.9, and δ is between 0 and 2.

0. Specific surface area is 1.5 m² ２ / g or more 100.0m ２ The proton-conducting composite oxide powder according to claim 1, wherein the amount is less than or equal to / g. 　 The proton-conducting composite oxide powder according to claim 1 or 2, comprising 90% by volume or more of a composite oxide represented by the following compositional formula (1). BaSc ｘ M １－ｘ O ３－δ (1) Here, M is one or more elements selected from Mo and W, x is between 0.6 and 0.9, and δ is between 0 and 2.

0. Sc ２ O ３ , BaCO ３ and the proton-conductive composite oxide powder according to claim 3, wherein the total content of graphite is less than 5% by volume. A precipitation step to obtain a precipitate by adding at least one aqueous solution of hydrochloric acid-based aqueous solution and nitric acid-based aqueous solution, which contains Ba ions, Sc ions, and ions of element M (where M is one or more elements selected from Mo and W), and has a pH of less than 2, to an alkaline aqueous solution, thereby adjusting the pH of the alkaline aqueous solution to 10 or more and less than 14. Alternatively, a precipitation step is performed by adding at least one aqueous solution of a hydrochloric acid-based aqueous solution and a nitric acid-based aqueous solution, which contain Ba ions and Sc ions and have a pH of less than 2, to an alkaline aqueous solution containing ions of element M (where M is one or more elements selected from Mo and W), thereby adjusting the pH of the alkaline aqueous solution to 10 or more and less than 14 to obtain a precipitate. A drying step of drying the precipitate at a predetermined temperature to obtain a precursor powder, and A method for producing a proton-conducting composite oxide powder, comprising a calcination step of calcining the precursor powder at a temperature of 700°C or higher. 　 The precursor powder is BaCO ３ or Ba(OH) ２ The process further includes a mixing step of mixing with to obtain a mixture, The method for producing a proton-conducting composite oxide powder according to claim 5, wherein the calcination step involves calcining the mixture. 　 The mixing step involves the precursor powder and the BaCO3. ３ or Ba(OH) ２ The mixing ratio of the precursor powder and the BaCO2 is such that the mass ratio is 1:X (where X is less than 2.0). ３ or Ba(OH) ２ Mix them together, The method for producing a proton-conducting composite oxide powder according to claim 6, wherein the firing step involves firing the mixture under firing conditions of a firing temperature of 800°C or more and 1500°C or less and a firing time of 1 hour or more.

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