JP2011228009A - Solid electrolyte fuel cell composite oxide, solid electrolyte fuel cell binder, solid electrolyte fuel cell electrode, solid electrolyte fuel cell collector member, solid electrolyte fuel cell, solid electrolyte fuel cell stack, and manufacturing method of solid electrolyte fuel cell composite oxide mixture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell electrode improved in electrode efficiency by providing a member with which a triple-phase interface can be easily formed although reducing costs as further as possible, while using a perovskite-type composite oxide as an electrode constituent material.SOLUTION: The present invention relates to a solid electrolyte fuel cell composite oxide comprised of a composite oxide mixed powder obtained by mixing at least two kinds of perovskite-type (ABO) composite powders, wherein the first composite oxide powder has a granularity distribution only in a range of 1 to 10 μm and the coefficient of variation (indicated by average diameter (μm)/standard deviation (μm)×100) of the distribution is less than 40%, and further, wherein the second composite oxide powder has a granularity distribution (frequency diameter) in the area of at least 1 to 10 μm and also has the granularity distribution (frequency diameter) in the range of 10 to 100 μm, namely, the compound oxide powder having two frequency diameters at least in the granularity distribution is used.

Description

  The present invention relates to a perovskite complex oxide for a solid oxide fuel cell electrode.

Next-generation energy has been widely studied and proposed as an alternative to fossil fuels that are currently widely used in industrial and household equipment. Among these next-generation energies, fuel cells can generate chemical energy and convert this chemical energy into electrical energy with high conversion efficiency. When fossil fuel is used, carbon dioxide (CO ₂ ) is exhausted. On the other hand, in this fuel cell, there is theoretically no CO ₂ emission, and water (H ₂ O) is simply generated as the emission. Only. For this reason, attention is spreading to fuel cells.

  In addition, since the fuel cell has a small influence on the efficiency of conversion of electric energy by the scale, studies on a wide range of applications such as driving an automobile and a stationary type in each home are progressing. There is a great expectation for technology related to such applications.

  In particular, solid oxide fuel cells (SOFC = Solid Oxide Fuel Cell; hereinafter simply referred to as SOFC) not only have high heat generation efficiency, but also waste heat discharged at high temperatures can be used for cogeneration, etc. Increases efficiency. Furthermore, since the SOFC operates at a high temperature, the electrode reaction can be sufficiently accelerated without using a noble metal such as platinum. Due to the above, the degree of attention to SOFC is high.

  By the way, an SOFC having a general structure has a structure in which a plurality of cells formed by sandwiching a solid electrolyte between a fuel electrode and an oxygen electrode are electrically connected by a current collecting member (for example, Patent Documents). 1). A technique is also known in which a plurality of cells are stacked to form a cell stack (see, for example, Patent Document 2).

The electrode material of the oxygen electrode needs to be composed of a material that is chemically stable in a high temperature atmosphere having an oxygen partial pressure of about 10 ⁻¹⁵ to 10 ⁻¹⁰ atm or more and that exhibits high electrical conductivity. However, when a general metal is used, there is a possibility that a problem of reduction in electrical conductivity due to metal oxidation may occur. Therefore, for example, a conductive perovskite complex oxide is used as an electrode material (see, for example, Patent Document 3). As a result, the value as a solid electrolyte fuel cell member is increasing.

  Note that a metal or an alloy is used for the current collecting member for connecting the cells to each other, which may cause the same problem as the electrode material. For this reason, attempts have been made to carry perovskite complex oxide on the surface of the current collecting member.

  As described above, in designing a fuel cell in which a perovskite-type composite oxide is used as a current collecting member or an electrode material, in order to produce a high-performance fuel cell, which part of the electrode reaction and how It is extremely important to proceed through a simple route. When the path is analyzed here, in the SOFC using the electrode material made of the perovskite complex oxide, the oxygen ion conductivity is lower in the air than in the electrode or the electrolyte. Therefore, a three-phase interface (TPB = Triple Phase Boundary) of an electrode, an electrolyte, and a gas is a main path of the electrode reaction. As a result, it can be said that how to form the three-phase interface, which is the active site of the electrode reaction, affects the activity of the fuel cell.

  Various techniques have been proposed as methods for increasing this activity. For example, a method of forming a cermet electrode by mixing and sintering an electrode material powder and an electrolyte material is known. Further, as a technique disclosed by the present applicant, a technique for increasing the specific surface area of the perovskite complex oxide and improving the reaction efficiency between the gas and the electrode is known (for example, see Patent Document 4).

  In addition, although it is a related technique, in order to increase the joining strength between an electrode and a current collection piece like patent document 1, the technique which makes an electrode material and a joining material the same substance is known. Further, as a technique for increasing the strength of the electrode itself, a technique is known in which a coarse film portion is formed by a thermal spraying method, and then a small particle size film portion is formed on the coarse film portion by a wet method (for example, patents). Reference 5).

Patent No. 2511121 JP 2009-110739 A JP 2005-179168 A Japanese Patent Laid-Open No. 2006-12764 JP-A-7-22033

  As described above, while various improvements have been made to the perovskite complex oxide, demands for the performance of the fuel cell itself are increasing day by day. Therefore, there is a possibility that a fuel cell having a higher performance than that of an existing fuel cell may be required. For that purpose, more than the members constituting the cell, particularly the electrode constituent materials described in Patent Document 4 and the like. It is assumed that high performance is required.

  If the electrodes can be configured by simple operation, it is expected that the unit cost of solids, which is currently hindering the spread of fuel cells, can be reduced, and as a result, energy resources that are friendly to the global environment can be provided at low cost. Conceivable.

  Accordingly, an object of the present invention is to provide a fuel cell electrode excellent in electrode efficiency by providing a member that can form a three-phase interface easily while being as low as possible. did.

  As a result of studying electrode materials for solving the above-mentioned problems, the present inventors have come to the conclusion that the powder described in Patent Document 4 is not sufficient to form a three-phase interface. Therefore, rather than a composite oxide having a high specific surface area value as described in the document, it is fired in a state where a plurality of particle groups coexist to form a three-phase interface. The present inventors have found the possibility that an electrode surface having suitable and appropriate pores can be formed, and completed the present invention.

The above object can be solved by the following means.
That is, the present invention is composed of a composite oxide mixed powder obtained by mixing at least two kinds of perovskite type (ABO ₃ ) composite powder, and the first composite oxide powder has a particle size distribution only in the range of 1 to 10 μm. And the distribution thereof has a coefficient of variation (indicated by mean diameter (μm) / standard deviation (μm) × 100) of less than 40%, and at least 1 to 10 μm as the second composite oxide powder. A composite oxide having a particle size distribution (frequency diameter) in the region between them and also having a particle size distribution (frequency diameter) in the range of 10 to 100 μm, that is, a composite having at least two frequency diameters in the particle size distribution. It is composed of a mixture of oxide powders.

  In particular, it is preferable that the mixing ratio of the first composite oxide powder and the second composite oxide powder is higher in the mass ratio of the second composite oxide powder than the first composite oxide powder. .

  In particular, the composition of the constituent materials of the first and second complex oxide powders is the same, and the A site of the perovskite complex oxide is composed of at least one kind of rare earth element and alkaline earth element, and the B site is It is preferably composed of at least two kinds of transition elements.

In addition, the first composite oxide powder described above has a contraction rate when it is heat treated at 1000 ° C. for 120 minutes in the air in the form of pellets (obtained by pressing and molding at 200 kgf / cm ² with a diameter of 15.0 mm). The composite oxide powder is 5% or more.

  The composite oxide mixed powder having the above properties includes an electrode used as a bonding agent for a fuel cell, a current collecting member having a surface formed by the powder, and a fuel cell and a cell stack in which they are used Can be provided.

  The substance is obtained by adding an aqueous alkali carbonate solution to a raw material solution of a perovskite complex oxide to form an amorphous precursor which is a carbonate, and subjecting the amorphous precursor to a heat treatment. A step (b) of forming a crystalline perovskite complex oxide, a wet pulverization of the crystalline perovskite complex oxide, having a particle size distribution only in the range of 1 to 10 μm, and a coefficient of variation of the distribution ( A step (c) of forming a first composite oxide powder having an average diameter (μm) / standard deviation (μm) × 100) of less than 40%, and the steps (a) and (b) And forming a second composite oxide powder having a particle size distribution (frequency diameter) in a region of at least 1 to 10 μm and also having a particle size distribution (frequency diameter) in the range of 10 to 100 μm. (D) the first composite oxide It can be obtained end and the second composite oxide powder and mixing the by (e).

  In the method for producing the perovskite complex oxide, the heat treatment of the precursor for precipitating the perovskite crystal from the precursor in the step (b) is preferably performed in a temperature range of 900 to 1500 ° C.

  In the method for producing the perovskite complex oxide, it is preferable that the wet pulverization treatment for obtaining the first perovskite complex oxide powder in the step (c) is performed by a sand grinder.

  By using the composite oxide mixture according to the present invention, it becomes possible to form a fuel cell electrode that is easier to form a three-phase interface than in the prior art when forming a sintered body.

It is a figure which shows the particle size distribution of the 1st complex oxide powder in the Example of this invention, and the perovskite type complex oxide in a comparative example. It is an integration figure of the particle size distribution of the 1st complex oxide powder in the example of the present invention, and the perovskite type complex oxide in the comparative example.

  Hereinafter, the composite oxide for a solid oxide fuel cell according to the present embodiment, a method for producing the same, and a bonding agent, an electrode, a current collecting member, a fuel cell, and a fuel cell stack using the same will be described in detail.

<Particle composition>
First, the composition of the perovskite complex oxide according to this embodiment will be described. The perovskite complex oxide has an ABO _3-δ structure as a structure. At this time, δ represents an oxygen deficiency amount including 0, and the range of the value of δ is preferably 0 ≦ δ <1.

  The A site mentioned here is preferably composed of at least one of rare earth elements such as La and alkaline earth metals such as Ba and Sr. The B site is preferably at least one selected from transition metals.

  Specifically, the A site is preferably selected from one rare earth element and one from an alkaline earth metal element. As the rare earth element here, any one of La, Pr, Nd, Sm, Eu, and Gd is preferable. Moreover, it is preferable to select any one of Ba, Sr, and Ca as the alkaline earth metal element. Here, the composition ratio (rare earth element / alkaline earth metal element) is 1.0 or more, preferably 1.2 or more, and more preferably 1.25 or more. This is because the perovskite structure can be suitably maintained within the above range.

  The B site is selected from transition metals as described above, but it is appropriate that the B site is composed of a plurality of types rather than a single type. In particular, it is preferably composed of two kinds of transition metal elements. When these two kinds of transition metal elements are T1 and T2, respectively, when the element number is T1 <T2, the composition ratio (T1 / T2) is 1.0 to 5.0, preferably 1.0 to 4.5, More preferably, it is preferable to set it as the range of 2.0-4.0. This is because the perovskite structure can be suitably maintained within the above range, as in the case of the A site.

  The composition ratio of the A site and the B site is A / B = 0.95 to 1.05, preferably 0.97 to 1.03, more preferably 0.99 to 1.01 in consideration of the structural balance. It is good to be. This is because the perovskite structure can be suitably maintained within the above range.

The composition relating to the perovskite complex oxide can be evaluated by the following method. That is, the composition other than iron, which is one of the transition metal elements, can be quantified by dissolving the powder and, for example, using a high-frequency induction plasma emission spectrometer ICP (IRIS / AP) manufactured by Nippon Jarrell Ash Co., Ltd. . About iron, a sample is dissolved and it can quantify with the Hiranuma automatic titration apparatus (CONTIME-980 type | mold) by Hiranuma Sangyo Co., Ltd., for example.
In addition to the composition evaluation method as described above, the measurement method of each parameter described in the following paragraphs is a measurement method applied not only to the present embodiment but also to the examples.

<Particle size>
Here, the mixing ratio of the first composite oxide powder and the second composite oxide powder contained in the fuel cell composite oxide of the present invention is such that the mass ratio of the second composite oxide powder is larger than that of the first composite oxide powder. It is preferable that the oxide powder has a higher ratio. Hereinafter, the first and second composite oxide powders are also simply referred to as first and second composite oxides.

  The “frequency diameter” in the present invention refers to a place having the highest frequency on a volume basis at a certain particle diameter when the particle size distribution is measured. The “particle frequency region” is a convex region having the “frequency diameter” as a vertex in the graph of particle size distribution. In the “particle frequency region”, the frequency decreases with the “frequency diameter” at the top, but the portion that becomes the “particle frequency region” in the present embodiment refers to the particle size from the “frequency diameter” portion. The part up to the part where the particle size distribution curve starts to form a convex region again when the entire distribution graph is viewed is defined as a “particle frequency region”.

  By mixing and using the first composite oxide particles and the second composite oxide particles as in this embodiment, coarse particles (so-called second composite oxide particles) are formed near the oxygen electrode surface in the fuel cell. In addition, small-diameter particles (so-called first composite oxide particles) can enter between coarse particles. Compared with coarse particles, fine particles with a small average particle size can be sintered at a relatively low temperature, so that even a relatively low temperature heat treatment can bridge the coarse particles by sintering. become. As a result, moderate pore portions are present between coarse particles, and as a result, a three-phase interface can be suitably formed.

  The “particle frequency region” in the first and second composite oxides mentioned here is represented by the following specific numerical values based on the particle size distribution measured by a laser scattering / diffraction particle size distribution measuring apparatus. That is, the particle frequency region in the first composite oxide has a frequency diameter in the range of 1 to 10 μm. The particle frequency region ending with the second composite oxide has a frequency diameter in the range of 1 to 10 μm and the coarse particle frequent diameter peak region in the range of 10 to 100 μm. At this time, regarding the volume ratio to the total volume of the perovskite complex oxide, the volume ratio of the particles at the frequency diameter in the first composite oxide is 1. It is preferably 3% or higher. Within this range, small particles can enter between an appropriate amount of coarse particles without having too many coarse particles, so that the particles can be effectively bonded.

  In addition to the “particle frequency region” in the first and second composite oxides, another particle frequency region may exist between the “particle frequency regions” in the first and second composite oxides. . In some cases, a powder having a larger average particle diameter may be added to have at least three large and small particle frequency regions.

  The small-diameter “particle frequency region” is preferably constructed based on one peak. The particle size range of the small particle “particle frequency region” is 1 to 10 μm as described above, and more preferably 1.5 to 5.0 μm. If this upper limit is not exceeded, the sintering temperature of the particles will not be excessively high, and the bonding effect between the particles can be exhibited effectively. On the other hand, if the lower limit is not exceeded, moderately small-sized particles remain at the interface portion of the coarse particles, and good bonding between the particles can be obtained.

  Further, the standard deviation indicating the particle size distribution of the particle size (in some cases, the aggregate size) is preferably 0.50 to 1.50 (μm), and preferably 0.75 to 1.25 (μm). If this upper limit is not exceeded, the dispersion | variation in particle | grains can be suppressed. As a result, the behavior during sintering becomes uniform, and the adhesion effect between the particles can be obtained effectively.

The average particle size of the particles can be measured with a laser scattering / diffraction particle size distribution measuring device manufactured by Beckman Coulter. In addition, in order to prevent the particles from being crushed by ultrasonic waves and calculate the agglomeration diameter, ultrasonic waves are not used during measurement. The optical model uses a real part 2.07 and an imaginary part 3. A sodium hexametaphosphate aqueous solution is used as a dispersion medium in the measurement. Using ₅₀ value D for the measurement of the average particle size, after calculating the standard deviation, the value of average particle size / standard deviation × 100, and calculates the coefficient of variation.

<Specific surface area of particles>
Moreover, the specific surface area value by the BET single point method of the perovskite type complex oxide particles according to the present embodiment is 6.0 to 11.0 m ² / g, and preferably 6.0 to 8.0 m ² / g. is there. If this upper limit is not exceeded, the particles will be reasonably fine. Then, the same effect as when the particle size range of the small diameter frequent peak region is not below the lower limit, that is, the effect that the small particles remain moderately in the interface portion of the coarse particles, between the particles A good bond can be obtained. In addition, the effect of not increasing the viscosity when the perovskite complex oxide is slurried can be expected. On the other hand, when it does not fall below the lower limit of the specific surface area value, it indicates that the particle diameter is not too large or that the particle surface has moderate irregularities. In this case, when the slurry is formed, small-diameter particles can moderately enter between coarse particles, and the occurrence of slurry unevenness due to the difference in particle diameter can be suppressed.

  In addition, the specific surface area of particle | grains is measured using a BET single point method, and a measuring apparatus can be measured, for example with 4 sorb US made from a Yua Sonics Corporation.

<Shrinkage rate>
Further, regarding the shrinkage rate of the perovskite type complex oxide particles (first complex oxide) according to the present embodiment, the shrinkage rate of the particles when heat-treated at 1000 ° C. for 120 minutes in the atmosphere is 5% or more. Is preferable, and 5 to 20% is more preferable. If this upper limit is not exceeded, it is possible to prevent the shrinkage from causing cracks on the electrode surface without the single shrinkage rate being too large. On the other hand, if the diameter is not below this lower limit, the small-diameter particles contract appropriately, so that when the small-diameter particles are used as a binder between the coarse particles, the contact between the coarse particles and the small-diameter particles can be brought close to surface contact. By increasing the contact area in this way, as a result, the three-phase interface that is the active site of the electrode reaction can be increased, and a large amount of current can be passed.

The shrinkage rate is measured under the following conditions. That is, the perovskite complex oxide is fired to obtain a powder. And it shape | molds in the pellet form of (phi) 15.0mm on the pressurization conditions of 200 kgf / cm < ² >. After calculating the diameter (A) of the particles in the pellet, the pellet is left in the atmosphere at 1000 ° C. for 120 minutes. This causes the pellets to shrink, and calculates the diameter (B) after firing. Then, the shrinkage rate is calculated by the formula of (A−B) / A × 100 (%). In addition, it is also possible to calculate the shrinkage rate per temperature change by changing the heat treatment conditions.

<Bulk density>
Furthermore, the bulk density of the perovskite complex oxide particles according to this embodiment is preferably 1.25 to 1.80 g / cc, more preferably 1.50 to 1.80 g / cc. By setting it within this range, the composite oxide according to the present invention is arranged in the void portion of the particle, so that the particles can be effectively bonded to each other, and thus the perovskite-type composite oxide is provided. This also improves the bondability between the electrode surface and the electrolyte.

  The bulk density can also be measured according to JIS standard Z-2512: 2006 (metal powder-tap density measurement method), but in this embodiment, according to the method described in JP-A-2007-263860. Is measured.

<Method for producing perovskite complex oxide>
Hereinafter, a method for producing a perovskite-type solid oxide fuel cell composite oxide will be described. In this embodiment, an aqueous alkali carbonate solution is added to the raw material solution of the perovskite complex oxide to form an amorphous precursor that is a carbonate, and the amorphous precursor is subjected to a heat treatment. A step (b) of forming a crystalline perovskite complex oxide and a step (c) of wet crushing the crystalline perovskite complex oxide to form a first complex oxide having a uniform particle size Then, the steps (a) and (b) are carried out, and the particle size distribution (frequency diameter) is at least in the region between 1 and 10 μm, and the particle size distribution (frequency diameter) is also in the range of 10 to 100 μm. A step (d) of forming such a second composite oxide, and a step (e) of mixing the uniform particle size oxide and the crystalline perovskite composite oxide formed in step (d). Is going.

(Amorphous precursor formation step [step (a)])
First, regarding the amorphous precursor formation step (step (a)), in the perovskite complex oxide ABO _3-δ , a substance containing a component of A site and a substance containing a component of B site are used. Mix. The concentration of each substance at this time is preferably 0.01 to 0.60 mol / L, more preferably 0.01 to 0.50 mol / L. If this upper limit is not exceeded, an amorphous substance can be easily obtained, and the viscosity of the slurry obtained after neutralization with an aqueous alkali carbonate solution does not increase. Therefore, productivity can be maintained when the post process is performed. Further, since the viscosity does not increase even when the slurry is aged, the possibility of precipitation of the crystalline substance can be reduced.

  After mixing the A-site and B-site constituent component-containing materials, an aqueous alkali carbonate solution is preferably added to obtain an amorphous precipitate from this liquid. As this aqueous alkali carbonate solution, it is preferable to use, for example, a precipitating agent comprising an alkali carbonate or a carbonate containing ammonium ions. As such a precipitating agent, sodium carbonate, sodium hydrogen carbonate, ammonium carbonate, ammonium hydrogen carbonate, or the like can be used. If necessary, a base such as sodium hydroxide or ammonia can be added to ammonium hydrogen carbonate or the like. Further, after forming a precipitate using sodium hydroxide, ammonia or the like, carbon dioxide gas may be blown. This makes it possible to obtain an amorphous material that is a precursor of a high specific surface area perovskite complex oxide. Furthermore, when a reducing agent is added in addition to such a precipitating agent, an amorphous precursor material having a higher specific surface area can be obtained. As the reducing agent, it is preferable to use a hydrogen generating compound such as hydrazine or sodium borohydride.

  Note that a material such as alumina, silica, titania, zirconia, or a heat-resistant material such as a composite oxide thereof can be added to the precursor material as long as the effect of the present embodiment is not hindered. In this case, an amorphous material in which these heat-resistant materials are intervened in the perovskite complex oxide is obtained.

  The amorphous material thus formed becomes a precursor for producing a perovskite complex oxide. In addition, as described above, the amorphous precursor is made of an amorphous substance containing a rare earth element, an alkaline earth metal element, and a transition metal element. A large amount of this amorphous precursor can be obtained by a so-called wet method in which a carbonate containing alkali and carbon dioxide gas is added to a mixed aqueous solution of such substances to produce a neutralized product. Therefore, the wet method is industrially suitable.

  In this embodiment, in order to form this amorphous precursor, the liquid temperature during the reaction needs to be low. Specifically, the liquid temperature is preferably 60 ° C. or lower, more preferably 45 ° C. or lower, and particularly preferably 30 ° C. or lower in the course of the reaction. If the liquid temperature does not exceed this upper limit, it is possible to suppress the risk of becoming a well-known crystalline substance such as a hydroxide and form an amorphous precursor. In addition, since it is reaction in aqueous solution, in order to ensure the fluidity | liquidity of a reaction system, it is preferable to perform reaction more than the freezing point of water, ie, 0 degreeC or more.

  Further, the pH of the reaction solution in forming the amorphous precursor is preferably 6 or more, more preferably alkaline. This is because in this embodiment, an amorphous material is obtained by using a neutralization reaction. Conversely, if it is acidic, it is difficult to obtain an amorphous substance, which is not preferable.

  The produced precipitate is preferably separated into solid and liquid by filtration, centrifugal sedimentation, decantation, etc., and washed with water to reduce the residual impurity ions. The obtained amorphous precipitate is dried by a method such as natural drying, heat drying, or vacuum drying, and after the drying treatment, pulverization treatment or classification treatment is performed as necessary.

(Amorphous precursor heat treatment step [step (b)])
Next, as for step (b), a crystalline perovskite complex oxide is obtained by heat-treating the precursor material formed in step (a). The heat treatment temperature is not particularly limited as long as a perovskite complex oxide can be obtained, but it may be 900 to 1500 ° C., preferably about 950 to 1300 ° C. The heat treatment is preferably performed in the air or in an oxidizing atmosphere.

  Thus, by passing through steps (a) and (b), a perovskite complex oxide for coarse particles having a particle diameter peak in a particle size distribution of at least 1 to 10 μm and a range of 10 to 100 μm is obtained. Can do.

(Wet grinding process [process (c)])
Next, as for step (c), the perovskite type complex oxide used in the present embodiment is subjected to wet crushing again after pulverizing the perovskite type complex oxide thus obtained. You can get things.

  The wet pulverization method used to obtain the particles according to the present invention includes the above-mentioned wet pulverization or wet crushing with a wet ball mill, sand grinder, attritor, pearl mill, ultrasonic homogenizer, pressure homogenizer, optimizer, etc. A perovskite complex oxide that meets the conditions can be formed. In particular, it is preferable to use a sand grinder.

  When selecting a sand grinder for wet grinding, any of the existing sand grinders such as the vertical flow pipe bead mill, the horizontal flow pipe bead mill, and the strong crushing type turbulent bisco mill should be used. Although it is pulverizable, a horizontal sand grinder is preferably used. The horizontal flow pipe type bead mill is preferable because it is uniformly crushed while staying in the vessel compared to the vertical flow pipe type bead mill, and more uniform crushing is possible at the same flow rate. is there. Further, the horizontal flow pipe type bead mill is economically preferable because it has a larger treatment flow rate than the strong pulverization type rush flow type visco mill.

  As the grinding media, it is preferable to use balls made of a hard material such as glass, ceramic, alumina, zirconia. The particle diameter of a ball for obtaining a perovskite complex oxide having a desired particle diameter is preferably about 0.1 to 5.0 mm, and more preferably 0.5 to 1.5 mm.

By passing through the above steps (a) to (c), the particle size distribution has a particle size distribution only in the range of 1 to 10 μm, and more than the perovskite complex oxide for coarse particles (that is, the second complex oxide). It is possible to obtain a perovskite-type composite oxide that is small and has a coefficient of variation of less than 40% for bonding between coarse particles. This composite oxide becomes the first composite oxide.
If the coefficient of variation is less than 40%, the average particle diameter is sufficiently uniform, and fine particles made of the first composite oxide can be used for the coupling between coarse particles.

(Second Composite Oxide Preparation Step [Step (d)])
In the present embodiment, separately from the first composite oxide, steps (a) and (b) are performed, and a second composite oxide not prepared for step (c) is prepared. By this step (d), a perovskite complex oxide having a particle size distribution (frequency diameter) in a region of at least 1 to 10 μm and a particle size distribution (frequency diameter) in the range of 10 to 100 μm is obtained. Can do.

(Mixing step [step (e)])
In the present embodiment, the perovskite complex oxide (first complex oxide) for bonding between the coarse particles and another crystalline perovskite complex oxide (second complex) obtained in the step (d) are used. Mixed oxide). Thereby, the perovskite complex oxide according to the present embodiment can be obtained.

<Application of perovskite complex oxide>
The perovskite complex oxide produced here can be applied to a solid oxide fuel cell (SOFC). Specifically, the present invention can be applied to SOFC electrodes, current collecting members, fuel cells, fuel cell stacks, and the like. Among these, in this embodiment, a fuel cell stack will be described.

  The fuel cell stack has a plate-like, rod-like (long) solid electrolyte fuel cell having a gas flow path in the length direction, and a direction perpendicular to the length direction of the fuel cell (cell thickness direction). Are arranged at a predetermined interval.

This fuel battery cell is provided with an oxygen electrode layer and a fuel electrode layer, and an electrolyte layer is provided between them. The electrolyte layer only needs to have a gas barrier property for preventing ions from moving inside and preventing leakage between the fuel gas and the oxygen gas. Examples thereof include polymer films and rare earth element stabilized zirconia, particularly Y ₂ O ₃ + ZrO ₂ . In addition, an interconnector is provided between the oxygen electrode layer of a certain cell and the fuel electrode layer of an adjacent cell.

  In the present embodiment, the perovskite complex oxide in the present embodiment is provided for the oxygen electrode layer. The aspect of the configuration can be changed as appropriate. For example, the composite oxide mixture may be applied and sintered. This process may be performed not only on the fuel electrode but also on the oxygen electrode side.

  Furthermore, instead of using platinum for the electrode, the electrode itself may be a sintered perovskite-type composite oxide paste. At this time, a metal catalyst such as platinum or an alloy catalyst may be used for electrode preparation. In addition, carbon black may be used as a catalyst support in order to improve the degree of metal dispersion.

  A current collecting member that electrically connects the fuel cells in series is disposed between the flat surfaces of the adjacent fuel cells. The current collecting member is joined to the oxygen electrode (fuel cell electrode) of one fuel battery cell and to the interconnector of the other fuel battery cell.

  In the present embodiment, the surface of the current collecting member is composed of a perovskite complex oxide. Further, instead of the current collecting member, a bonding agent for bonding the fuel cell electrode of one fuel cell and the interconnector of the other fuel cell may be used. As the bonding agent, it is preferable to use the perovskite complex oxide in the present embodiment.

  As mentioned above, although this embodiment was explained in full detail, according to this embodiment, there exist the following effects.

  That is, by mixing wet pulverized oxide even if the particle size is small and mixing the oxide whose particle size is irregular without wet pulverization treatment, the volume ratio of the small particle size is reduced. A relatively increased perovskite type complex oxide is used for an electrode for a fuel cell, a current collecting member and the like. As a result, coarse particles are present near the surface of the oxygen electrode in the fuel cell, and small particles can enter between the coarse particles. In addition, since the small-diameter particles are very uniform, the coarse particles and the small-diameter particles can be favorably bound, and as a result, the coarse particles can be favorably bound to each other. As a result, the three-phase interface can be formed stably and satisfactorily, and the electrode reaction can be efficiently caused. Ultimately, a fuel cell electrode, a current collecting member, a fuel cell, and a fuel cell stack having excellent electrode efficiency are obtained. Furthermore, by using only the perovskite type complex oxide, an electrode, a current collecting member and the like having excellent electrode efficiency can be formed without performing a plurality of steps, which can contribute to cost reduction.

  As mentioned above, although embodiment which concerns on this invention was mentioned, said disclosure content shows exemplary embodiment of this invention. The scope of the present invention is not limited to the exemplary embodiments described above. Whether or not explicitly described or suggested herein, those skilled in the art will make various modifications to the embodiments of the present invention based on the disclosure of the present specification. Can be implemented.

Examples according to the present invention will be described below.
<Example 1>
(Amorphous precursor formation step [step (a)])
First, in order to form an amorphous precursor, lanthanum nitrate hexahydrate (La (NO3) 3 · 6H ₂ O) 4.47 kg, strontium nitrate (Sr (NO ₃ ) ₂ ) 1.61 kg, iron nitrate the nonahydrate _{(Fe (NO 3) 3 ·} 9H 2 O) 5.58kg, cobalt nitrate hexahydrate _{(Co (NO 3) 2 ·} 6H 2 O) 1.12kg respectively deionized water 102.2kg After dissolution, a mixed solution A of nitrate was prepared. At this time, the concentration of these solutions was about 0.20 mol / L in total of dissolved species.

  Next, 36.6 kg of ion-exchanged water and 8.33 kg of ammonium carbonate were inserted into the dissolution tank, and the water temperature was adjusted to 15 ° C. while stirring.

  Thereafter, an ammonium carbonate solution was gradually added to the solution A to carry out a neutralization reaction, thereby depositing an amorphous precursor of perovskite. Thereafter, the amorphous precursor was aged for 30 minutes to complete the reaction. The obtained substance was washed with water and dried by a conventional method to obtain a dry powder of perovskite amorphous precursor.

(Amorphous precursor heat treatment step [step (b)])
Next, in order to obtain a crystalline perovskite complex oxide by firing the amorphous precursor, the obtained dry powder was fired in the air at 1000 ° C. for 2 hours. Thus, a crystalline composite oxide having a perovskite form was obtained from the amorphous precursor. The obtained composite oxide was subjected to dry crushing treatment with a pin mill.

(Wet grinding process [process (c)])
Next, in order to pulverize the crystalline perovskite complex oxide to obtain an oxide having a uniform particle size, the fired powder obtained in the step (b) and pure water were mixed. Then, a mixture of the baked powder and pure water was put into a gallon sand grinder filled with zirconia beads of φ1.0 mm as a medium at a filling rate of 30%. Then, the grinding | pulverization process for 1 hour was performed at 1500 rpm. And perovskite type complex oxide was obtained by performing media removal, water washing, and drying by the usual method.

In addition, the particle | grains obtained by the process (c) were calculated with the specific surface area measurement by BET method as 6.8 m < ² > / g. The bulk density was 1.62 g / cc, and it was confirmed from the X-ray diffraction pattern that the composite oxide had a perovskite structure.

Moreover, when the particle size distribution analysis (volume ratio (volume%)) was performed with respect to the particle | grains obtained by the process (c), the particle size distribution as shown in FIG. 1 was obtained. It can be seen that particles are present in the range of 1 to 10 μm and constitute a mountain distribution. The average particle diameter _{(D 50} diameter) is 2.9 .mu.m. The standard deviation (σ) was 1.19 μm, and the coefficient of variation was 39.4%. The particle shrinkage (1000 ° C.) was 7.1%. FIG. 2 shows the particle size distribution of FIG.

(Second Composite Oxide Preparation Step [Step (d)])
Then, separately from the first complex oxide, the steps (a) and (b) were performed, and a second complex oxide not prepared for the step (c) was prepared. By this step (d), a perovskite complex oxide having a particle size distribution (frequency diameter) in a region of at least 1 to 10 μm and a particle size distribution (frequency diameter) in the range of 10 to 100 μm is obtained. I was able to. In addition, the particle size etc. of the 2nd complex oxide obtained at this process (d) correspond to the comparative example 1 of FIG.1 and FIG.2.

(Mixing step [step (e)])
Then, the perovskite complex oxide for bonding between coarse particles (first complex oxide) and another crystalline perovskite complex oxide (second complex oxide) obtained in the step (d). Mixed. Thus, the perovskite complex oxide according to this example was obtained.

  The perovskite complex oxide according to this example was sintered. The electrical conductivity was measured for this sintered body. As a result, good results were obtained.

<Examples 2-3>
The perovskite complex oxide was the same as in Example 1 except that the pulverization time for the crystalline perovskite complex oxide in step (c) was 2 hours in Example 2 and 3 hours in Example 3. Formed. In any of the examples, the uniform particle size oxide after the step (c) had a particle size distribution having a single peak as shown in FIG. FIG. 2 shows the particle size distribution of FIG.
Table 1 shows a summary of the grinding conditions in step (c) up to Examples 1-3.

  Further, the perovskite complex oxide according to Examples 2 and 3 was sintered to obtain a sintered body. The electrical conductivity was measured for this sintered body. As a result, good results were obtained in both Examples 2 and 3.

<Comparative Example 1>
In Comparative Example 1, a perovskite complex oxide was formed using the same method as in Example 1 except that the wet grinding (c) and mixing step (d) of Example 1 were not performed.

The composite oxide particles obtained in Comparative Example 1 were calculated to be 4.3 m ² / g by specific surface area measurement by the BET method. The bulk density was 1.92 g / cc, and it was confirmed from the X-ray diffraction pattern that the composite oxide had a perovskite structure.

In addition, as described in the second composite oxide preparation step (d), when the particle size distribution analysis was performed on the composite oxide particles obtained in the comparative example, a particle size distribution as shown in FIG. 1 was obtained. It was. It can be seen that a wide range of particles are present in the range of 0.5 to 100 μm, and at least a bimodal distribution is formed. The average particle diameter _{(D 50} diameter) is 17.63Myuemu. The standard deviation (σ) was 17.04 μm and the coefficient of variation was 82.0%. Further, the shrinkage rate of the particles (1000 ° C.) was 3.2%. FIG. 2 shows the particle size distribution of FIG.

<Comparative example 2>
In Comparative Example 2, pulverization was performed in the same manner as in Example 1 except that the pulverizing means was a dry vibration ball mill (amplitude ± 5.0 mm, vibration frequency 1000 rpm). The obtained results are shown in FIG. 1, and the particle size distribution in an integrated diagram is shown in FIG. As shown in the figure, particles having a small particle size and a uniform particle size distribution could not be obtained. The average particle diameter _{(D 50} diameter) is 11.12Myuemu.

  In the same manner as in Example 1, the perovskite complex oxide in the comparative example was sintered. The electrical conductivity was measured for this sintered body. As a result, it was inferior to the results of Examples 1 to 3.

  The perovskite complex oxide having the above-mentioned physical properties obtained by the production method according to the present invention has suitable properties as a member for a fuel cell, and more specifically, an electrode for a fuel cell, a current collecting member, a fuel cell, and a fuel cell stack Can be configured.

Claims (12)

A composite oxide for a solid oxide fuel cell, comprising a composite oxide mixed powder obtained by mixing at least two perovskite (ABO ₃ ) composite powders.
However, the composite oxide mixed powder means that the first composite oxide powder has a particle size distribution only in the range of 1 to 10 μm, and the distribution is a coefficient of variation (average diameter (μm) / standard deviation (μm). X2) is less than 40%, and the second composite oxide powder has a particle size distribution (frequency diameter) in a region of at least 1 to 10 μm, and in the range of 10 to 100 μm. Is a composite oxide powder having a particle size distribution (frequency diameter), that is, a composite oxide powder having two frequency diameters at least in the particle size distribution.   The mixing ratio of the first composite oxide powder and the second composite oxide powder is a ratio by which the second composite oxide powder is higher in mass ratio than the first composite oxide powder. The composite oxide for a solid oxide fuel cell as described.   The composition of the constituent materials of the first and second composite oxide powders is the same, and the A site of the perovskite complex oxide is composed of at least one of a rare earth element and an alkaline earth element, and the B site is a transition. The composite oxide for a solid oxide fuel cell according to claim 1 or 2, comprising at least two elements. The first composite oxide powder is in the form of pellets (obtained by pressing and molding at 200 kgf / cm ² with a diameter of 15.0 mm) and has a shrinkage ratio of 5% or more when heat treated at 1000 ° C. for 120 minutes in the atmosphere. The composite oxide for a solid oxide fuel cell according to any one of claims 1 to 3, wherein the composite oxide powder is.   A bonding agent for a solid oxide fuel cell, wherein the composite oxide for a solid oxide fuel cell according to claim 1 is used.   An electrode for a solid oxide fuel cell, wherein the composite oxide for a solid oxide fuel cell according to any one of claims 1 to 4 is used.   A current collecting member for a solid oxide fuel cell, wherein the composite oxide for a solid oxide fuel cell according to any one of claims 1 to 4 is used.   A solid oxide fuel cell using the composite oxide for a solid oxide fuel cell according to claim 1.   A solid oxide fuel cell stack using the composite oxide for a solid oxide fuel cell according to claim 1.   A step (a) of adding an alkali carbonate aqueous solution to the raw material solution of the perovskite-type composite oxide to form an amorphous precursor which is a carbonate; and heat-treating the amorphous precursor to form a crystalline perovskite Step (b) of forming a type composite oxide, wet pulverizing the crystalline perovskite type composite oxide, having a particle size distribution only in the range of 1 to 10 μm, and a variation coefficient (average diameter (μm ) / Standard deviation (μm) × 100) is less than 40% to form the first composite oxide powder (c), and the steps (a) and (b) are performed, and at least 1 A step (d) of forming a second composite oxide powder having a particle size distribution (frequency diameter) in a region between 10 μm and a particle size distribution (frequency diameter) in a range of 10 to 100 μm; The first composite oxide powder, and Step of mixing the second composite oxide powder containing (e), a manufacturing method of the solid oxide fuel cell composite oxide mixtures.   11. The solid electrolyte type according to claim 10, wherein in the method for producing a perovskite complex oxide, the heat treatment of the precursor for precipitating the perovskite crystal from the precursor in the step (b) is performed in a temperature range of 900 to 1500 ° C. 11. A method for producing a composite oxide mixture for a fuel cell.   12. The solid electrolyte according to claim 10, wherein in the method for producing a perovskite complex oxide, the wet pulverization treatment performed to obtain the first perovskite complex oxide powder in the step (c) is performed by a sand grinder. For producing a composite oxide mixture for a fuel cell

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