JP7381248B2 - Nickel-ion conductive ceramic mixed powder and composition thereof - Google Patents

Description

The present invention relates to a nickel-ceramic mixed powder and a composition containing the mixed powder.

In recent years, with the aim of developing a sustainable society, functional materials with low environmental impact and low pollution have been actively developed, and electrode materials and catalyst materials are gaining importance due to their wide range of applications. The required characteristics for these are common, and from the perspective of efficiently utilizing energy, emphasis is placed on operational efficiency.

Recently, metal-ceramic composite materials are increasingly being used as materials for these functional materials. Metal-ceramic composite materials have porous frameworks in which metals and ceramics are mixed, and it is possible to design materials in which metals, ceramics, and the gas phase in contact with them each have separate roles, making them suitable for electrode and catalyst applications. It is known to exhibit useful reaction activity. For example, if we design materials to give metals electrical conductivity and catalytic activity, and ceramics to give ionic conductivity, the raw material gas supplied from the gas phase and the ions supplied from the ceramic layer will react with the metal as a catalyst. By doing so, it can be used in battery electrode reactions that extract electrons and chemical substance synthesis reactions.

As the first example of such functional materials, solid oxide fuel cells (hereinafter also referred to as SOFC) are popular due to their advantages such as high efficiency power generation and the ability to use low-purity fuel gas without any problems. , stationary power sources for home and business use, and distributed power plant applications are being actively developed. The structure of a SOFC battery cell is such that an air electrode (also called a cathode) and a fuel electrode (also called an anode) face each other with an electrolyte substrate made of ion-conductive ceramics in between, and the air electrode separates oxygen from oxygen. A reaction occurs to generate oxygen ions, and a reaction occurs at the fuel electrode to extract electrons from the oxygen ions and hydrogen.

SOFC fuel electrodes generally use as a starting material a mixture of nickel oxide and ion conductive ceramic particles having a particle size ranging from submicron to micron. An electrode made of the mixture of the oxides is formed on an electrolyte substrate, and then the nickel oxide particles and the ion-conductive ceramic particles are sintered together by air firing (about 1300° C.) to form a porous body. Since this process involves an oxidizing atmosphere, nickel oxide powder is mainly used as the nickel source for the fuel electrode.

During actual use, hydrogen reduction treatment (approximately 800°C) is performed to reduce nickel oxide to metallic nickel. This is because metallic nickel is a catalyst that causes an electrode reaction, and the above-mentioned electrode reaction does not occur in the state of nickel oxide. Through this series of atmospheric firing and hydrogen reduction processes, a porous electrode made of metallic nickel and ion-conductive ceramics is constructed, and a three-phase interface between metallic nickel, ion-conductive ceramics, and gas phase is formed. , it becomes possible to perform the function as a fuel electrode of SOFC. Patent Document 1 discloses a fuel electrode for a solid oxide fuel cell using an electrode material in which electrolyte particles with a diameter of 0.1 to 0.5 μm and nickel oxide particles with a diameter of 0.5 μm to 1.5 μm are mixed in a specific ratio. The team aims to improve battery performance by lowering the resistance between the fuel electrode and the electrolyte substrate.

As a second example, solid oxide electrolytic cells (hereinafter also referred to as SOEC) are attracting attention as a clean and sustainable hydrogen production technology. It can exhibit performance with the same structure as the above-mentioned SOFC, and can synthesize hydrogen using water as a raw material by causing a reverse reaction to the chemical reaction that occurs within the SOFC.
Chemical reactions at the fuel electrode during SOFC operation (called cathode during SOEC operation):
H ₂ +O ^2- →H ₂ O+2e ^-
Chemical reactions at the air electrode during SOFC operation (called anode during SOEC operation):
1/2O ₂ +2e ^- →O ^2-

Since the structure of SOEC is the same as that of SOFC, the materials used in SOFC are often used instead. For example, in Patent Document 2, an SOEC is fabricated using nickel oxide particles with a particle size of 0.6 μm and SrZr _0.5 Ce _0.4 Y _0.1 O _0.1 as ion-conductive ceramic particles, and hydrogen is Discloses that it can be manufactured.

Furthermore, other examples that require materials and properties similar to those of the above-mentioned functional materials include reforming catalysts that produce hydrogen by decomposing hydrocarbon compounds through steam reforming reactions. Metal-ceramic composite materials that catalyze synthesis reactions are attracting attention.

JP2009-266713A Japanese Patent Application Publication No. 2018-172763

Currently, due to the ever-increasing demand for technologies with low environmental impact, functional materials made from composite materials of metals and ceramics are expected to operate even more efficiently, and improvements in operating efficiency and catalytic activity are required. . However, since there are limits to improving efficiency by adjusting equipment operating conditions, there was a need for fundamental performance improvement technology that goes into the materials.

The first way to increase the efficiency of functional materials such as electrodes and catalysts made from metal-ceramic composite materials is to increase the catalytic reaction. The second measure is to improve the efficiency of electron transport by metals and ion transport by ion-conducting ceramics, since when the flow of electrons and ions stagnates, it becomes reaction rate limiting and reduces the operating efficiency of the material. It is also important to

Taking SOFC as an example, at the SOFC fuel electrode, metal nickel acts as a catalyst at the three-phase interface of metal nickel, ion-conductive ceramics, and gas phase, allowing the hydrogen oxidation reaction (H ₂ + O ²⁻ → H ₂ O+2e ⁻ ) is generated.

In the current SOFC fuel electrode material, we use relatively large particles of submicron to micron size as the raw material nickel oxide powder, so we have developed a technology that allows for We believe that there is a problem in that the number of phase interfaces is insufficient, which limits the improvement of the catalytic activity of the electrode.

In addition, current materials mainly use nickel oxide as a nickel source, but since the sintering temperature of oxides is higher than that of metals, sufficient sintering of nickel oxide particles does not occur during atmospheric firing, so hydrogen Even after reduction, a sufficient conductive path between the metal nickel was not formed, resulting in poor conductivity, that is, a large ohmic resistance value.

These two issues, catalytic activity and electrical conductivity, need to be met at the same time because if only one of them is superior, it will not be sufficient to improve the operating efficiency of the material.

Although we have explained SOFC as an example here, similar issues may arise with materials whose mechanism of action is chemical reactions at three-phase interfaces and electron transport by metals, and the above issues are common to SOECs, catalysts, etc. do.

In order to solve the above problems, the present inventors focused on a mixed powder of fine metal nickel particles (A) and fine ion-conductive ceramic particles (B). In the prior art, since the material is produced through firing in an atmospheric atmosphere, it is assumed that nickel oxide, which has already been oxidized, is used as a raw material. The present inventors have discovered that the sinterability of metallic nickel particles can be improved by using metallic nickel as a raw material, and furthermore, the median diameter is as fine as 10 nm or more and 200 nm or less; By using a mixed powder of fine ion-conductive ceramic particles of 200 nm or less in size, when used, it improves conductivity by improving metal connectivity, i.e., reduces ohmic resistance, and improves catalytic activity, i.e., charge by increasing the number of three-phase interfaces. The present invention was completed based on the discovery that it is possible to simultaneously reduce the movement resistance value and improve the operating efficiency as a functional material. The gist of the invention is as follows.

(1) Metallic nickel particles (A) with a median diameter of 10 nm or more and 200 nm or less,
ion conductive ceramic particles (B) having a median diameter of 10 nm or more and 200 nm or less,
An electrode material or an electrode material characterized in that the content of nickel element and the content of ion conductive ceramics are in a volume ratio of [nickel element]/[ion conductive ceramics] = 20/80 to 80/20. Nickel-ion conductive ceramic mixed powder used in catalysts .
(2) The nickel-ion conductive ceramic mixed powder used in the electrode material or catalyst according to (1), further comprising nickel-containing particles (C) having a median diameter of 300 nm or more and 10 μm or less.
(3) The nickel-ion conductive ceramic mixed powder used in the electrode material or catalyst according to (1) or (2), further comprising ion conductive ceramic particles (D) having a median diameter of 300 nm or more and 10 μm or less.
(4) The volume content of the metal nickel particles (A) and the nickel-containing particles (C) satisfy the relationship of volume content of the particles (A)>volume content of the particles (C), and (2), or (2) the volume content of the ion conductive ceramic particles (B) and the ion conductive ceramic particles (D) satisfy the relationship: volume content of the particles (B) > volume content of the particles (D); Nickel-ion conductive ceramic mixed powder used for the electrode material or catalyst described in (3).
(5) A particle composition for use in an electrode material or catalyst, which contains 20% by weight or more and 95% by weight or less of the mixed powder according to any one of (1) to (4), and further contains a solvent.

By using at least one of the mixed powders or compositions thereof of the present invention, high catalytic activity, i.e., low charge transfer resistance, and high conductivity, i.e., low ohmic resistance, can be achieved at the same time, resulting in a reduction in internal resistance. , the operational efficiency as a functional material can be improved.

The mixed powder of the present invention has metal nickel particles (A) which have a finer particle size than those of the prior art, and ion conductive ceramic particles (B) which have a finer particle size than those of the prior art. It is characterized by a combination of.

Contains metallic nickel particles (A) with a median diameter of 10 nm or more and 200 nm or less, and ion conductive ceramic particles (B) with a median diameter of 10 nm or more and 200 nm or less, and the content of nickel element and the content of ion conductive ceramics. The volume ratio of [nickel element]/[ion conductive ceramic] = 20/80 to 80/20 reduces the ohmic resistance value and increases the number of three-phase interfaces when used as a SOFC electrode. A high effect of improving the catalytic activity, that is, reducing the charge transfer resistance value can be obtained. By combining all of the constituent particle types, appropriate median diameter range, and content ratio of nickel element and ion-conductive ceramics, high effects can be obtained and usage performance can be significantly improved. .

The mechanism is as follows. We focused on the three-phase interface, where the three phases of nickel, ion-conductive ceramics, and gas phase come into contact, as active points for nickel-based catalytic reactions, and thought that increasing the number of points would lead to higher catalytic activity. When the mixed powder of the present invention is used as a raw material, fine metal nickel particles (A) (hereinafter sometimes simply referred to as "particles (A)") and fine ion-conductive ceramic particles (B) ( Hereinafter, it may be simply abbreviated as "particles (B)"), so that the metal nickel particles and the ion-conductive ceramic particles can be finely and densely integrated on the substrate. This makes it possible to increase the three-phase interface of metal nickel/ion conductive ceramic/gas phase when the product reaches a usable stage after undergoing atmospheric firing and hydrogen reduction. Therefore, since the number of reaction active sites increases, the catalyst activity can be increased and the charge transfer resistance value can be reduced.

In the present invention, the particles (A) are characterized in that they are nano-level fine metallic nickel. As a result, electron conduction occurs efficiently during use, and as a result, the ohmic resistance value can be reduced. As a more practical effect, for example, when used as a fuel electrode of SOFC, power generation efficiency can be improved.

The mechanism is as follows. Because the particles (A) are metallic nickel, sintering of metallic nickel particles begins to occur at a lower temperature in the atmospheric firing process compared to the conventional case of using nickel oxide with a large particle size, and the nickel particles The connecting part (necking part) tends to become thick. As a result, even during use, the connecting portions between the metal nickel particles become thicker, making it possible to improve conductivity.

The mixed powder of the present invention is characterized in that the metal nickel particles (A) have a median diameter of 10 nm or more and 200 nm or less, and the ion-conductive ceramic particles (B) have a median diameter of 10 nm or more and 200 nm or less; , catalytic activity can be increased, charge transfer resistance can be reduced, and power generation efficiency can be increased. Preferably, the median diameter of the metal nickel particles (A) is 30 nm or more and 150 nm or less, and the preferable range of the particle diameter of the ion-conductive ceramic particles (B) is 30 nm or more and 150 nm or less, which has the effect of reducing charge transfer resistance. becomes higher.

The mechanism is as follows. When the median diameter of the metallic nickel particles (A) and the ion-conductive ceramic particles (B) is 10 nm or more and 200 nm or less, the number of contact points between the metallic nickel and the ion-conductive ceramic during use is increased and three The number of phase interfaces can be increased and the catalytic activity can be increased. If the median diameter of the metal nickel particles (A) and the ion-conductive ceramic particles (B) is 30 nm or more and 150 nm or less, the effect will be more pronounced. On the other hand, if the median diameter of the metal nickel particles (A) is less than 10 nm or the median diameter of the ion-conductive ceramic particles (B) is less than 10 nm, the volumetric shrinkage that occurs during particle sintering becomes large, so The contact points between the nickel and the ion-conducting ceramic particles decrease, the catalytic activity decreases, and the charge transfer resistance increases. In addition, if the median diameter of the metal nickel particles (A) exceeds 200 nm or the median diameter of the ion-conductive ceramic particles (B) exceeds 200 nm, the specific surface area of the particles decreases. Catalytic activity decreases due to decreased contact points between conductive ceramic particles.

The effect of the present invention is expressed by the median diameter of the primary particles of the metal nickel particles (A) and the ion-conductive ceramic particles (B), and the secondary particles of the particles (A) and the median diameters of the particles (B) There is no problem even if it exists as a secondary particle or a secondary particle of particles (A) and (B). Here, a primary particle refers to a single particle that is not aggregated, and a secondary particle refers to an aggregated particle.

Particles (A) are metallic nickel if elemental analysis is performed on the cross section of the particle (A) using TEM-EDS, and 80% by weight or more of the nickel element is detected in the center of the cross section of the particle (A). Refers to things. If the nickel element is contained at 80% by weight or more at the center of the cross section of the particle (A), the sinterability of the metal nickel particles is sufficiently ensured, so any impurities other than the nickel element may be included. For example, it may contain carbon, oxygen, metals other than nickel, etc. Moreover, one or both of nickel oxide and nickel hydroxide may be present on the surface of the metal nickel particles (A). The presence of one or both of nickel oxide and nickel hydroxide on the surface prevents reactions such as rapid oxidation of the particles, making them safe to handle. Note that, as long as the thickness of one or both of nickel oxide and nickel hydroxide is 10 nm or less, the above-mentioned advantage of sinterability is not impaired.

In the present invention, the ion conductive ceramics constituting the particles (B) and the particles (D) described below are made of known ion conductors whose single crystal bulk conductivity at 1000° C. is 10 ⁻³ S/cm or more. Ceramics. Examples of ceramics having such ion conductivity include stabilized zirconias represented by yttria-stabilized zirconia and scandia-stabilized zirconia, and ceria-based solid solutions represented by samaria-doped ceria.

In the mixed powder of the present invention, the volume ratio of the nickel element to the ion conductive ceramic is within the range of 20/80 to 80/20. This makes it possible to achieve both high catalytic activity and high conductivity during use.

This mechanism can be explained as follows. In the mixed powder containing fine metallic nickel particles (A) and fine ion-conductive ceramic particles (B), the volume ratio of nickel element to ion-conductive ceramics is within the range of 20/80 to 80/20. For example, both the total value of the specific surface area of the metal nickel particles and the total value of the specific surface area of the ion-conductive ceramic particles can be made sufficiently large.

Therefore, it is possible to simultaneously achieve the characteristic that the number of three-phase interfaces during use is greater than in the past, and the characteristic that nickel and ion conductive ceramics, which are necessary for conductivity, are not interrupted within the material. This feature is not exhibited by the combination of particles with relatively large particle sizes, which is the conventional technique. If the content of nickel or ion conductive ceramics is less than 20% by volume, the nickel or ion conductive ceramics will be interrupted within the material and sufficient conductivity will not be obtained, resulting in an increase in ohmic resistance. .

The volume ratio of the nickel element to the ion conductive ceramic can be calculated from the measurement results of ICP emission spectrometry. The method will be explained below using a combination of nickel element and yttria-stabilized zirconia as an example.

The weight ratio of nickel element and yttria-stabilized zirconia can be calculated by ICP emission spectrometry. In yttria-stabilized zirconia, yttrium and zirconium are detected separately, but the weight ratio of yttrium and zirconium obtained from ICP emission spectrometry is converted into Y ₂ O ₃ and ZrO ₂ , respectively, and Y ₂ O ₃ and ZrO By summing the weight ratios of ₂ , the weight ratio of yttria-stabilized zirconia can be calculated.

Next, the weight ratio of each of the nickel element and yttria-stabilized zirconia is converted to a volume ratio by dividing it by the solid density at room temperature (especially around 25 ° C.), and the volume ratio of the nickel element and yttria-stabilized zirconia is calculated. (Hereinafter, the solid density at room temperature will be simply referred to as "solid density"). The solid density of elemental nickel is 8.9 g/ ^cm3 , and the solid density of yttria-stabilized zirconia is 6.0 g/ ^cm3 . Even if the ion-conductive ceramic is zirconia stabilized by other oxide species (e.g. scandia-stabilized zirconia) or ceria-based (e.g. samaria-doped ceria), the volume ratio of nickel element to yttria-stabilized zirconia Similar to the calculation method described above, the volume ratio can be calculated by dividing the weight ratio by the solid density.

Since particles (A) and particles (B) are the main components of the mixed powder of the present invention, the total volume of particles (A) and particles (B) is the nickel-ion conductive ceramic mixed powder of the present invention. It is preferable that the amount is 50% by volume or more based on the total body weight. Furthermore, it is preferable that both particles (A) and particles (B) contain 10% by volume or more.

In addition to the above particles (A) and (B), the mixed powder of the present invention also includes nickel-containing particles (C) having a larger median diameter of 300 nm or more (hereinafter simply referred to as "particles (C)"). ) may be included. This makes it possible to improve the conductivity and, as a result, reduce the ohmic resistance value.

This mechanism can be explained as follows. By combining particles (A) and (C) with different median diameters, it becomes possible to stack nickel particles on the substrate at a high filling rate. Therefore, when performing atmospheric firing, nickel is efficiently sintered, and the conductive path caused by nickel is prevented from being interrupted. Since this is maintained even after hydrogen reduction, the conductivity is improved during use, that is, the effect of reducing the ohmic resistance value is obtained. This effect cannot be obtained with the combination of nickel-containing particles (C) and ion-conductive ceramic particles (B). In order to obtain the effect of improving conductivity, the volume content of particles (C) is preferably 5% by volume or more and less than 50% by volume based on the total amount of the nickel-ion conductive ceramic mixed powder of the present invention.

If the median diameter is 300 nm or more, the nickel particle filling rate can be increased by combining with fine particles (A), which has the effect of reducing the ohmic resistance value during use. However, the median diameter of particles (C) is preferably 10 μm or less. If the median diameter exceeds 10 μm, for example, when mixed powder is used as an electrode, the electrode surface roughness will increase during use, and the adhesion with the current collector mounted on the electrode surface will decrease, resulting in poor conductivity. This may lead to deterioration of the resistance, that is, an increase in the ohmic resistance value. The effect of the particles (C) is to increase the filling rate of the particles due to the difference in particle size from the fine particles (A), so the material composition does not affect the effect. Therefore, both metal nickel and nickel oxide can be suitably used as the particles (C), and either one of them may be used, or both may be used in combination.

Further, the mixed powder of the present invention further includes fine particles in addition to the mixed powder containing the particles (A) and (B), or the mixed powder containing the particles (A), (B), and (C). The ion conductive ceramic particles (D) (hereinafter sometimes simply referred to as "particles (D)") having a larger particle size than the ion conductive ceramic particles (B) are used as the nickel-ion conductive ceramic of the present invention. It may be contained in a range of 5% or more and less than 50% based on the total amount of mixed powder. As a result, it is possible to improve the conductivity during use, that is, to reduce the ohmic resistance value.

This mechanism is as follows. By combining ion conductive ceramic particles (B) and (D) with different median diameters, the filling rate of the ion conductive ceramic particles can be increased. Therefore, during atmospheric firing, sintering between ion-conductive ceramic particles is further promoted, and during use, the conductivity is improved, that is, the ohmic resistance value is reduced. This effect cannot be obtained with the combination of particles (D) and metal nickel particles (A).

The presence of ion-conductive ceramic particles having a median diameter exceeding 300 nm can increase the filling rate of ion-conductive ceramic particles within the material, and has the effect of reducing the ohmic resistance value after hydrogen reduction. However, the median diameter of the particles (D) is preferably 10 μm or less. If the median diameter exceeds 10 μm, for example, when mixed powder is used as an electrode, the surface roughness of the electrode surface after hydrogen reduction will increase, resulting in a decrease in the adhesion between the current collector and the electrode, resulting in a value of ohmic resistance. This may lead to an increase in

The median diameter (D50 diameter) of particles (A), (B), (C), and (D) in the present invention is measured by the following cross-sectional observation method.

That is, a press-molded body of mixed powder or the like is filled with resin and cross-sectionally processed, and the cross-sectional image is observed using SEM or TEM. First, the composition of the particles is observed using SEM-EDS or TEM-EDS surface analysis, point analysis, etc., and it is determined whether the particle type is nickel or ion conductive ceramic. For example, if the main metal component of the particle to be observed is nickel, it can be determined that it is a nickel particle, and if the main component is zirconium, it can be determined that it is stabilized zirconia.

Next, a cross-sectional image is taken, the cross-sectional area on the two-dimensional image of the particle is calculated using image analysis software (for example, image analysis software Image Pro Premier 9.2 (manufactured by Media Cybernetics)), and the area equivalent to the calculated area is calculated. The median diameter is the radius of a circle having an area (hereinafter referred to as "circle equivalent diameter") and the median value when arranged in descending order. At least 200 particles are analyzed. Boundaries between particles are determined by image processing using image analysis software. If different particles (for example, A and B) are in contact with each other, they are excluded from the measurement. In addition, measurements where the area of the particle is 1 pixel x 1 pixel or less on the SEM or TEM image are excluded from analysis, as this is the smallest unit of the number of pixels in the SEM or TEM image, and this impairs measurement accuracy. do.

When calculating the equivalent circle diameter, all particles in the cross-sectional image are subject to analysis, and particles with an equivalent circle diameter of less than 250 nm are classified as particles (A) or (B), and particles with an equivalent circle diameter of 250 nm or more are classified as particles. Classify as (C) or (D). Particles having an equivalent circular diameter of less than 250 nm are classified into particles (A) and particles (B) by methods such as surface analysis and point analysis described above. Particles having an equivalent circular diameter of 250 nm or more are also classified into particles (C) and particles (D) by methods such as surface analysis and point analysis described above. It should be noted that the order of the step of distinguishing particles (A) to (D) and the step of distinguishing equivalent circle diameters of less than 250 nm or 250 nm or more does not matter.

Subsequently, the median diameter of particles less than 250 nm is calculated, and the median diameters of particles (A) and particles (B) are determined, respectively. Furthermore, the median diameter of particles of 250 nm or more is calculated, and the median diameters of particles (C) and particles (D) are determined, respectively.

As mentioned above, in the mixed powder of the present invention, the volume ratio of nickel element to ion conductive ceramics is within the range of 20/80 to 80/20, but nickel-containing particles (C), ion conductive ceramics When using particles (D), consider the following.

The volume of the nickel element is converted into volume using the solid density of nickel from the sum of the weight of the nickel element contained in the metal nickel particles (A) and the weight of the nickel element contained in the nickel-containing particles (C). When using nickel oxide particles as the nickel-containing particles, the calculation is performed excluding oxygen. The volume of the ion-conductive ceramic is converted into volume from the sum of the weights of the ion-conductive ceramic particles (B) and the ion-conductive ceramic particles (D) using the solid density of the ion-conductive ceramic.

In addition, the sum of the weight of the nickel element contained in the metal nickel particles (A) and the weight of the nickel element contained in the nickel-containing particles (C), the ion conductive ceramic particles (B) and the ion conductive ceramic particles (D) The total weight of can be calculated using the same method as described above using the measurement results of ICP emission spectroscopy. The total weight of nickel element contained in particles (A) and particles (C) is calculated by ICP emission spectrometry. Furthermore, the total weight of the chemical components constituting each of the particles (B) and particles (D) is calculated by ICP emission spectrometry. In calculating the volume ratio, there is no need to distinguish between particles (A) and particles (C), or between particles (B) and particles (D). In order to express the effects of the present invention, the total volume of the nickel element and the total volume of the ion conductive ceramics contained in the mixed powder are effective, and the volume ratio is within the range of 20/80 to 80/20. It has been confirmed that, if present, a high effect of improving the ohmic resistance and charge transfer resistance described above can be obtained.

When at least one of particles (C) and particles (D) is used, the volume content of particles (A) and particles (C), and the volume content of particles (B) and particles (D) are as follows: It is preferable that the volume content of the particles (A) is greater than the volume content of the particles (C), and the volume content of the particles (B) is greater than the weight content of the particles (D).

The mechanism is as follows. If the volume content of particles (A) is greater than the volume content of particles (C), and the volume content of particles (B) is greater than the volume content of particles (D), then the particles (A) are fine. Since a sufficient number of fine particles (B) can be ensured to fill coarse voids and a sufficient number of contact points between nickel and ion-conductive ceramics can be ensured, it is possible to enhance the catalytic activity. Note that when either the particles (C) or the particles (D) are not used, the volume content of the unused particles is considered to be 0.

The size relationship of the contained volumes of particles (A) to (D) (hereinafter referred to as "order") and the ratio of the contained volumes of particles (A) to (D) shall be determined by the above-mentioned cross-sectional observation method. I can do it. The specific derivation procedure is as follows.

A press-molded body of mixed powder or the like is filled with resin and cross-sectioned, and the cross-sectional image is observed using SEM or TEM. First, the composition of the particles is analyzed using SEM-EDS or TEM-EDS surface analysis, point analysis, etc., and it is determined whether the type of particles is nickel or ion conductive ceramics. For example, if the main metal component of the particle to be observed is nickel, it can be determined that it is a nickel particle, and if the main component is zirconium, it can be determined that it is stabilized zirconia.

Next, the volume of the particles is calculated using the following method. A cross-sectional image is taken using SEM or TEM, and the cross-sectional area of the particle on the two-dimensional image is calculated using image analysis software (for example, image analysis software Image Pro Premier 9.2 (manufactured by Media Cybernetics)). The radius of a circle having an area equivalent to the calculated area (circle equivalent diameter) is calculated. The particle is considered to be a true sphere having this equivalent circle diameter, and the volume is calculated from the equivalent circle diameter.

Finally, the total value of this volume value for each particle (A) to (D) is determined as the volume content of each particle (A) to (D), and this ranking is determined as the content volume of each particle (A) to (D). The volume is determined as the order of volume, and the ratio of the volume content of particles (A) to (D) is determined as the ratio of volume content of particles (A) to (D). The range of cross-sectional observation is to observe an arbitrary region of at least 10 μm square in the cross-sectional image, and analyze all particles present in that region. As a result, variations in measurement are suppressed, and it is possible to accurately calculate the order and ratio of volumes contained in particles.

The mixed powder of the present invention may contain components other than particles (A), (B), (C), and (D) according to its specifications within a range that does not impede the effects of the present invention.

[Particle composition using mixed powder of the present invention]
The mixed powder of the present invention may be used in the form of a composition containing a solvent in addition to the particles. A state containing a solvent is generally called a slurry, paste, ink, or the like. When the mixed powder of the present invention is in the form of a composition containing a solvent, it is possible to use existing general-purpose coating film production techniques such as screen printing, inkjet, and spin coating depending on the viscosity of the material. and is industrially useful.

The solvent that can be used preferably has a boiling point of 100° C. or higher, from the viewpoint of preventing cracking of the material by drying the solvent gently. Examples of usable solvents include alcohol-based, aromatic-based, hydrocarbon-based, ester-based, ketone-based, ether-based, and amine-based solvents. Examples of alcoholic solvents include 1-heptanol, 1-octanol, 2-octanol, 2-ethyl-1-hexanol, 1-nonanol, 3,5,5-trimethyl-1-hexanol, 1-decanol, 1- Aliphatic alcohols with 7 or more carbon atoms such as undecanol and isobornylcyclohexanol, ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butane Diols, polyhydric alcohols such as 1,6-hexanediol, 1,8-octanediol, tetramethylene glycol, and methyl triglycol, terpineols such as α-terpineol, β-terpineol, and γ-terpineol, and ethylene glycol monomers. Propyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, methyl methoxybutanol, diethylene glycol, dipropylene glycol, 2-phenoxyethanol, 1-phenoxy-2-propanol Examples include alcohols having an ether group such as. Examples of hydrocarbon solvents include octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, benzene, toluene, xylene, and ethylbenzene. As the amine solvent, octylamine, oleylamine, etc. can be used. Additionally, water can also be used.

Further, the solvent contained in the composition may contain an additive (hereinafter, in the present invention, a solvent containing an additive is also simply referred to as a solvent). Examples of additives include viscosity modifiers, thixotropic agents, leveling agents, surfactants, and pore-forming agents. For example, viscosity modifiers include thermosetting resins such as phenol resins, epoxy resins, unsaturated polyester resins, urea resins, and melamine resins, polyethylene resins, acrylic resins, methacrylic resins, nylon resins, acetal resins, polyvinyl acetal resins, etc. Organic binders such as thermoplastic resins can be exemplified, and by using these organic binders, the viscosity of the solvent can be adjusted and are useful for further improving workability.

In the composition of the present invention, it is preferable that the content ratio of the mixed powder is 20% by weight or more and 95% by weight or less, with the remainder being the solvent. If the content ratio of the mixed powder exceeds 95% by weight, that is, if the content ratio of the solvent is less than 5% by weight, solid-liquid separation between the particles and the solvent will likely occur, which may significantly reduce workability. be. On the other hand, if the content ratio of the mixed powder is less than 20% by weight, that is, if the content ratio of the solvent exceeds 80% by weight, the viscosity of the composition may become too low and the workability may be significantly reduced.

The content ratio of the mixed powder in the composition can be measured using TG-DTA (differential thermal/thermogravimetric simultaneous measurement) based on the change in weight when the temperature is increased. Specifically, the solvent is removed by volatilization or decomposition by raising the temperature to 800°C while performing a nitrogen flow. As a result, the weight loss is the weight of the solvent and the remaining weight is the weight of the mixed powder. The content weight ratio of can be calculated.

Metal nickel particles (A) can be used regardless of the manufacturing method. For example, it is possible to use one obtained by a known method in which nickel ions are precipitated by heating reduction using a wet reduction method from a mixture containing a nickel salt and a chemical component having reducing ability. Alternatively, it may be produced using a gas atomization method or the like. Further, particles with a size of about submicrons (100 nm or more) can be produced by a pulverization method using micron-sized particles as a starting material.

The ion conductive ceramic particles (B) can be used regardless of the manufacturing method. For example, in the case of yttria-stabilized zirconia, commercially available products such as TZ-8Y manufactured by Tosoh Corporation can be used. It is also possible to synthesize, for example, a method for synthesizing stabilized metal-doped zirconia is to use a salt of an additive metal (for example, yttria for yttria-stabilized zirconia, or scandium for scandia-stabilized zirconia) and zirconium. Methods such as the coprecipitation method, which is synthesized from salts, can be mentioned. Further, particles with a size of about submicrons (100 nm or more) can be produced by a pulverization method using micron-sized particles as a starting material.

The nickel-containing particles (C) and the ion-conductive ceramic particles (D) can be used regardless of their manufacturing method, and commercially available products may be used. Specifically, the nickel-containing particles (C) include nickel powder manufactured by Kanto Kagaku (product number 28104-32), nickel manufactured by Kojundo Kagaku (product number NIE10PB), nickel manufactured by Aldrich (product number 268283), and nickel oxide manufactured by Toyo Technica (product number 268283). (Product name: NiO Fine Grade) etc. can be used. Alternatively, particles having a desired particle size may be produced using a pulverization method using coarse particles of about several tens of μm as a raw material. The ion-conductive ceramic particles (D) are yttria-stabilized zirconia powder manufactured by Toyo Technica (product name YSZ-8 Fine Grade), yttria-stabilized zirconia powder manufactured by Toyo Technica (product name YSZ-8 Standard Grade), and the first rare element. Industrial-made yttria-stabilized zirconia powder (product name: HSY-8), scandia-stabilized zirconia powder (product name: 10ScSZ TC Grade) manufactured by Toyo Technica, etc. can be used. Alternatively, particles having a desired particle size may be produced using a pulverization method using coarse particles of about several tens of μm as a raw material.

The mixed powder disclosed in the present invention can be prepared by preparing powders of particles (A), particles (B), particles (C), and particles (D), respectively, and then using a ball mill, a bead mill, a mixer, a mortar, or an autorotating machine. It can be produced by mixing using a revolving stirring device or the like and kneading with any solvent.

The method of forming an electrode using the mixed powder in the present invention is not particularly limited, as long as it is a method generally used for manufacturing SOFC, for example, when used in a SOFC fuel electrode. For example, it can be obtained by forming a paste coating film on an electrolyte substrate as a support by screen printing, doctor blade, etc., and then baking it (electrolyte support type). Alternatively, a method of forming a powder compact of mixed powder and forming an electrolyte layer on one surface of the compact can also be used (fuel electrode support type).

The firing temperature and time for firing the molded body of the mixed powder and the coating film of the composition are 1200 to 1500°C for 1 to 5 hours, and the preferred temperature is 1250 to 1450°C.

The mixed powder and its composition in the present invention can be applied, for example, to fuel electrode layers in various types of electrolyte-supported and metal-supported SOFCs, and to fuel electrode supports and fuel electrode layers in fuel-electrode supported SOFCs. . It is also applicable to proton conduction fuel cells. It can also be applied as a cathode of a solid electrolyte type water electrolysis cell. In addition, it can be applied to a wide range of catalytic applications, such as reforming catalysts for hydrocarbon compounds such as natural gas, dry reforming, and ammonia decomposition reactions.

[Evaluation of nickel-ion conductive ceramic mixed powder]
[Examples 1 to 32, Comparative Examples 1 to 13]
Nickel-ion conductive ceramic mixed powders of Examples 1 to 32 and Comparative Examples 1 to 13 having median diameters and ratios of particles (A) to (D) as described in Tables 1-1 to 1-4. was created. The method for producing the nickel-ion conductive ceramic mixed powders of Examples 1 to 32 and Comparative Examples 1 to 13 will be described below.

[Synthesis process of metal nickel particles (A)]
82 g of nickel acetate tetrahydrate was added to 200 g of oleylamine, heated to 140° C. under a nitrogen stream, and held for 180 minutes to obtain a complexing reaction solution. To this complexing reaction solution, 0.4 g of 20% phenyllithium (PhLi) dibutyl ether solution was added under a nitrogen stream, heated to 250 ° C. with a mantle heater, and further heated at 250 ° C. for 5 minutes. Metal nickel particles (A) were obtained. Using a transmission electron microscope (TEM) and an energy dispersive X-ray analyzer (EDS), it was confirmed that the metal nickel particles (A) contained 92% by weight of nickel element in their cross section.

The median diameter of the metal nickel particles (A) can be determined as shown in Table 1-1 by appropriately adjusting the blending ratio of the chemical substances used and the heating time within the range of 1 to 20 minutes in this step. It is possible to control the median diameter shown in Table 1-2.

[Preparation of ion conductive ceramic particles (B)]
As the ion conductive ceramic particles (B), commercially available products or synthetic products were used. As for particles with a median diameter of 40 nm, TZ-8Y manufactured by Tosoh Corporation was used as described above.

Particles having a median diameter other than 40 nm were produced by a coprecipitation method. The method for synthesizing yttria-stabilized zirconia and the method for adjusting the median diameter are as follows. After dissolving ZrO(NO ₃ ) ₂ ·xH ₂ O as a zirconium source and Y(NO ₃ ) ₃ ·6H ₂ O as an yttrium source in pure water, a sodium hydroxide aqueous solution having a pH of 13 was added dropwise. The supernatant solution of the precipitate was removed by decantation, and the precipitate was washed with ethanol and distilled water to isolate the target product, yttria-stabilized zirconia ("YSZ" in Table 1-1, etc.). The median diameter was controlled by adjusting the concentrations of ZrO(NO ₃ ) _{2.xH 2} O and Y(NO ₃ ) _{3.6H 2} O and the dropping rate of the aqueous sodium hydroxide solution.

The method for synthesizing scandia-stabilized zirconia and the method for adjusting the median diameter are as follows. After dissolving ZrO(NO ₃ ) ₂ ·xH ₂ O, which is a zirconium source, and Sc(NO ₃ ) ₃ , which is a scandium source, in pure water, an aqueous sodium hydroxide solution having a pH of 13 was added dropwise. The supernatant solution of the precipitate was removed by decantation, and the precipitate was washed with ethanol and distilled water to isolate the target scandia-stabilized zirconia ("ScSZ" in Table 1-1). Note that the median diameter was controlled by adjusting the concentrations of ZrO(NO ₃ ) _{2.xH 2} O and Sc(NO ₃ ) ₃ and the dropping rate of the aqueous sodium hydroxide solution. The conductivity of the single crystal bulk body of yttria-stabilized zirconia at 1000°C was 0.1 S/cm, and the conductivity of the single crystal bulk body of scandia-stabilized zirconia at 1000°C was 0.2 S/cm.

[Preparation of nickel-containing particles (C) and ion-conductive ceramic particles (D)]
The median diameter of the nickel-containing particles (C) and ion-conductive ceramic particles (D) was adjusted by using commercially available products and by grinding coarse particles. As the nickel-containing particles (C), for Examples 8 to 10, 12, 14 to 15, 17, 28, and Comparative Examples 4 and 6, Kojundo Kagaku nickel (product number NIE10PB) was used, and for Examples 16, 18 to 20 , 23-25, Comparative Examples 2, 8, and 10 using Aldrich nickel (product number 268283), Example 22 using Kanto Kagaku nickel powder (product number 28104-32), Examples 26-27, Comparative Example 1 For Comparative Examples 5 and 9, nickel oxide manufactured by Toyo Technica (product name: NiO Fine Grade) was used, and for Examples 29 to 30, nickel powder whose median diameter was adjusted by a pulverization method was used. As the ion conductive ceramic particles (D), for Examples 10 to 22, 24 to 28 and Comparative Examples 2, 4 to 6, and 8 to 10, yttria stabilized zirconia powder manufactured by Toyo Technica (product name YSZ-8 Fine Grade) was used. ), yttria-stabilized zirconia powder manufactured by Toyo Technica (product name YSZ-8 Standard Grade) for Example 23 and Comparative Example 1, and yttria-stabilized zirconia whose median diameter was adjusted by a pulverization method for Examples 31 and 32. As for the powder, in Example 28, Scandia stabilized zirconia powder (product name: 10ScSZ TC Grade) manufactured by Toyo Technica was used.

[Mixed powder production process]
The metal nickel particles (A) were isolated by replacing the solvent of the obtained metal nickel particles (A) with toluene and removing the toluene by drying. Ion-conducting ceramic particles (B), nickel-containing particles (C), or ion-conducting ceramics (D) were added to the metal nickel particles (A) to obtain a mixture of particles (A) to (D). . The mixing ratio of these particles (A) to (D) can be adjusted by adjusting the mixing ratio of ion conductive ceramic particles (B), nickel-containing particles (C) and ion conductive ceramic particles ( D) was adjusted by measuring the weight of each. However, the metal nickel particles (A), ion-conductive ceramic particles (B), nickel-containing particles (C), and ion-conductive ceramics (D) are converted into volume using the weight of the weighed particles and solid density. and added as shown in the content ratios (vol%) listed in Tables 1-3 and 1-4.

A mixture of particles (A) to (D) was kneaded using a bead mill to obtain a mixed powder of nickel-yttria stabilized zirconia.

[Measurement of median diameter and volume content]
An appropriate amount of the mixed powder was taken, embedded in epoxy resin, and cross-sectioned by cross-section polishing and FIB processing. Cross-sectional TEM observation of this sample was performed, and TEM observation of a 10 μm square area was performed. A field emission transmission electron microscope JEM-2100F (manufactured by JEOL Ltd.) was used for TEM, and a JED-2300T (manufactured by JEOL Ltd.) was used for EDS. Using TEM-EDS, it was determined whether each particle was nickel or an ion-conductive ceramic particle. A TEM image was taken and used for particle size measurement. The particle diameter was measured using image analysis software Image Pro Premier 9.2 (manufactured by Media Cybernetics). As a specific procedure for analyzing the particle size, the brightness, contrast, and gamma value of the image are adjusted, and then calibration data is created using the scale bar of the TEM. Set "area" as the measurement item and use the division command to detect particle boundaries. A count command was executed to determine the area of the particles, particle diameter=circle equivalent diameter=2×√(area÷pi), and the median diameter of the particles (ie, D50 value) was determined from this data. At this time, measurement values in which the particle area was 1 pixel x 1 pixel or less were judged to impair the accuracy of the measurement since this is the smallest unit of the number of pixels in a TEM image, and were excluded from the analysis. Also, using the equivalent circle diameter of each particle obtained here, calculate the volume of the particle = 4 ÷ 3 × pi × (equivalent circle diameter ÷ 2) ³ , and calculate the particle volume for each of particles (A) to (D). The volume content of each of particles (A) to (D) was calculated by taking the total, and the ratio of the volume content of particles (A) to (D) was determined.

The median diameter and content ratio (vol%) of the particles (A), the particles (B), the particles (C), and the particles (D) were as shown in Tables 1-1 to 1-4.

[Volume ratio of nickel element and ion conductive ceramics]
The mixed powder was subjected to ICP emission spectroscopy analysis according to the following procedure, and the volume ratio of nickel element to yttria-stabilized zirconia was calculated. First, the mixed powder was dissolved in an acid solution and subjected to ICP emission spectroscopy. From the obtained measured values, the weight ratio of nickel element to yttria-stabilized zirconia was calculated. By converting this value into a volume ratio using each solid density (8.9 g/cm ³ for nickel and 6.0 g/cm ³ for yttria-stabilized zirconia), the volume ratio of nickel element to yttria-stabilized zirconia is determined. was calculated. Using a similar method, the volume ratio of nickel element to scandia-stabilized zirconia was calculated. The results are shown in the columns of "nickel element content" and "ion conductive ceramic content" in Tables 1-3 and 1-4.

[Preparation process of electrolyte paste]
An electrolyte paste was prepared by mixing yttria-stabilized zirconia powder (manufactured by Tosoh, trade name TZ-8Y) with α-terpineol at a weight ratio of 3:1 and kneading in an agate mortar.

[Evaluation sample production process]
The produced mixed powder was filled into an 8 mmφ hot press mold, and a load of 0.1 t was applied for 3 minutes using a hand press machine to produce a mixed powder molded body. The amount of mixed powder used was adjusted so that the thickness of the mixed powder molded body was 500 μm. The previously prepared electrolyte paste was applied to one side of the mixed powder compact by screen printing, and dried on a hot plate at 100° C. for 30 minutes to remove the solvent. This sample was fired at 1400° C. for 2 hours (hereinafter, the fired mixed powder molded body will be referred to as mixed powder fired body). Pt paste (TR-7070 manufactured by Tanaka Kikinzoku Co., Ltd.) was applied to the opposite side of the mixed powder fired body across the electrolyte layer in a size of 6 mm by screen printing, and then heated at 1200°C for 2 hours. Fired. Furthermore, a platinum wire was wound around the side surface of this electrolyte layer to serve as a reference electrode, and an evaluation sample was prepared. Pt mesh was used as a current collector.

[evaluation]
The charge transfer resistance value and ohmic resistance value of this mixed powder fired body were measured by an AC impedance method. It can be said that the lower the charge transfer resistance value, the higher the catalytic activity, and the lower the ohmic resistance value, the higher the conductivity. The measurement temperature was 800° C., and the measurement frequency was 1 MHz to 0.01 Hz. Furthermore, 3% H ₂ O-97% H ₂ was passed through the mixed powder fired body side, and dry air was passed through the layer on the opposite side of the mixed powder fired body with the electrolyte in between.

[Evaluation criteria]
The charge transfer resistance value was compared and evaluated with the measured value of Comparative Example 1. Comparative Example 1 is a mixed powder consisting of nickel oxide particles with a median diameter of 1 μm and yttria-stabilized zirconia particles with a median diameter of 3 μm, and is an evaluation sample of the prior art. When compared with the measured value of Comparative Example 1, it was judged as ★ if it was 80% or less, ◎ if it was 85% or less, ○ if it was 90% or less, and × if it exceeded 90%. The ohmic resistance value is ★ if it is 80% or less compared to the measured value of Comparative Example 1, ◎ if it is 85% or less, ○ if it is 90% or less, and ○ if it is more than 90%. It was judged as ×.

Invention examples according to the present invention are Examples 1 to 32, Examples containing particles (C) are Examples 8 to 10, 12, 14 to 30, and Examples containing particles (D) are Examples 10 to 28. , 31, 32. Further, among the Examples containing particles (C) and (D), Examples 14 to 28 satisfy the relationship of volume content of particle (A) > volume content of particle (C), and the relationship of volume content of the particles (B)>volume content of the particles (D) is satisfied. Comparative Examples 1 to 13 show results in cases where the requirements for the nickel-ion conductive ceramic mixed powder of the present invention were not satisfied.

The mixed powders of Examples 1 to 32 according to the present invention are made of metal nickel particles (A) having a median diameter of 10 nm or more and 200 nm or less, and ion conductive ceramic particles (B) having a median diameter of 10 nm or more and 200 nm or less. Comparison with conventional technology that does not meet these requirements because the ratio of the volume of nickel element to the volume of oxide constituting the ion-conductive ceramic particles is within the range of 20/80 to 80/20. Compared to Example 1, it was confirmed that both high catalytic activity and high conductivity were achieved.

Further, in Examples 8 to 10, 12, and 14 to 28 containing nickel-containing particles (C) having a median diameter of 300 nm or more and 10 μm or less, it was confirmed that the conductivity was further improved. Furthermore, it was confirmed that in Examples 10 to 28, which were characterized by containing ion-conductive ceramic particles (D) having a median diameter of 300 nm or more and 10 μm or less, the conductivity was increased. Further, among Examples 8 to 28, the volume content of the metal nickel particles (A) is greater than the volume content of the nickel-containing particles (C), and the volume content of the particles (B) is greater than the volume content of the particles (D). It was confirmed that in Examples 9 and 13 to 28, which were characterized by a larger amount than the amount, the charge transfer resistance value was reduced.

[Evaluation of nickel-ion conductive ceramic composition]
[Examples 41 to 78, Comparative Examples 41 to 53]
Nickel-ion conductive ceramic compositions of Examples 31 to 78 and Comparative Examples 41 to 53 having the median diameter and content ratio of particles (A) to (D) as described in Tables 2-1 to 2-6. I made something. The method for producing the nickel-ion conductive ceramic compositions of Examples 31 to 78 and Comparative Examples 41 to 53 will be described below.

[Synthesis process of metal nickel particles (A)]
82 g of nickel acetate tetrahydrate was added to 200 g of oleylamine, heated to 140° C. under a nitrogen stream, and held for 180 minutes to obtain a complexing reaction solution. To this complexing reaction solution, 0.4 g of 20% phenyllithium (PhLi) dibutyl ether solution was added under a nitrogen stream, heated to 250 ° C. with a mantle heater, and further heated at 250 ° C. for 5 minutes. Metal nickel particles (A) were obtained. Using a transmission electron microscope (TEM) and an energy dispersive X-ray analyzer (EDS), it was confirmed that the metal nickel particles (A) contained 92% by weight of nickel element in their cross section.

In addition, the median diameter of the metal nickel particles (A) can be determined in Table 2-1 and Table 2-1 by appropriately adjusting the compounding ratio of the chemical substances used and the heating time within the range of 1 to 20 minutes in this step. It is possible to control the median diameter shown in 2-2.

[Preparation of ion conductive ceramic particles (B)]
As the ion conductive ceramic particles (B), commercially available products or synthetic products were used. As for particles with a median diameter of 40 nm, TZ-8Y manufactured by Tosoh Corporation was used as described above.
Particles having a median diameter other than 40 nm were produced by a coprecipitation method. The method for synthesizing yttria-stabilized zirconia and the method for adjusting the particle size are as follows. After dissolving ZrO(NO ₃ ) ₂ ·xH ₂ O as a zirconium source and Y(NO ₃ ) ₃ ·6H ₂ O as an yttrium source in pure water, a sodium hydroxide aqueous solution having a pH of 13 was added dropwise. The supernatant solution of the precipitate was removed by decantation, and the precipitate was washed with ethanol and distilled water to isolate the target product, yttria-stabilized zirconia ("YSZ" in Table 2-1, etc.). The median diameter was controlled by adjusting the concentrations of ZrO(NO ₃ ) _{2.xH 2} O and Y(NO ₃ ) _{3.6H 2} O and the dropping rate of the aqueous sodium hydroxide solution.

The method for synthesizing scandia-stabilized zirconia and the method for adjusting the median diameter are as follows. After dissolving ZrO(NO ₃ ) ₂ ·xH ₂ O, which is a zirconium source, and Sc(NO ₃ ) ₃ , which is a scandium source, in pure water, an aqueous sodium hydroxide solution having a pH of 13 was added dropwise. The supernatant solution of the precipitate was removed by decantation, and the precipitate was washed with ethanol and distilled water to isolate scandia-stabilized zirconia ("ScSZ" in Table 2-1), which was the target product. Note that the median diameter was controlled by adjusting the concentrations of ZrO(NO ₃ ) _{2.xH 2} O and Sc(NO ₃ ) ₃ and the dropping rate of the aqueous sodium hydroxide solution. The conductivity of the single crystal bulk body of yttria-stabilized zirconia at 1000°C was 0.1 S/cm, and the conductivity of the single crystal bulk body of scandia-stabilized zirconia at 1000°C was 0.2 S/cm.

[Preparation of nickel-containing particles (C) and ion-conductive ceramic particles (D)]
The median diameter of the nickel-containing particles (C) and ion-conductive ceramic particles (D) was adjusted by using commercially available products and by grinding coarse particles.
As the nickel-containing particles (C), for Examples 50 to 52, 54, 56 to 59, 61, 74, and Comparative Examples 44 and 46, Kojundo Kagaku nickel (product number NIE10PB) was used, and for Examples 60, 62 to 65 , 67-69, Comparative Examples 42, 48, 50, Aldrich nickel (product number 268283), Example 66, Kanto Kagaku nickel powder (product number 28104-32), Examples 70-73, Comparative Example 41 For Comparative Examples 45 and 49, nickel oxide manufactured by Toyo Technica (product name: NiO Fine Grade) was used, and for Examples 75 to 76, nickel powder whose median diameter was adjusted by a pulverization method was used.
As the ion conductive ceramic particles (D), for Examples 52 to 67, 68 to 74, and Comparative Examples 42, 44 to 46, and 48 to 50, yttria stabilized zirconia powder manufactured by Toyo Technica (product name YSZ-8 Fine Grade) was used. ), yttria-stabilized zirconia powder manufactured by Toyo Technica (product name YSZ-8 Standard Grade) for Example 67 and Comparative Example 41, and yttria-stabilized zirconia whose median diameter was adjusted by a pulverization method for Examples 77 and 78. For Example 74, Scandia stabilized zirconia powder (product name: 10ScSZ TC Grade) manufactured by Toyo Technica was used as the powder.

[Mixed powder production process]
The metal nickel particles (A) were isolated by replacing the solvent of the obtained metal nickel particles (A) with toluene and removing the toluene by drying. Ion-conducting ceramic particles (B), nickel-containing particles (C), or ion-conducting ceramics (D) were added to the metal nickel particles (A) to obtain a mixture of particles (A) to (D). . The mixing ratio of these particles (A) to (D) can be adjusted by adjusting the mixing ratio of ion conductive ceramic particles (B), nickel-containing particles (C) and ion conductive ceramic particles ( D) was adjusted by measuring the weight of each. However, the metal nickel particles (A), ion-conductive ceramic particles (B), nickel-containing particles (C), and ion-conductive ceramics (D) are converted into volume using the weight of the weighed particles and solid density. It was added as shown in the content ratio (vol%) shown in Table 2-3 and Table 2-4.

The mixture of particles (A) to (D) was sufficiently kneaded using a bead mill to obtain a mixed powder of nickel-yttria stabilized zirconia.

[Composition production process]
To mixed powder (7.5 g) of nickel-yttria stabilized zirconia, 96 parts by weight of α-terpineol and 4 parts by weight of polyvinyl acetal resin (S-LEC BH-A; manufactured by Sekisui Chemical Co., Ltd.) as a binder resin were added. 2.5 g of the mixed solution was added and sufficiently kneaded in a mortar to obtain a composition (paste).

[Evaluation sample production process]
This composition was coated on a 200 μm thick yttria-stabilized zirconia substrate (electrolyte layer) with a size of 6 mm diameter by screen printing, and then fired at 1350°C in an air atmosphere for 2 hours to form a fired composition body. did. Pt paste (TR-7070, manufactured by Tanaka Kikinzoku Co., Ltd.) was applied to the opposite side of the fired composition body across the electrolyte layer by screen printing to a size of 6 mm, and then fired at 1200° C. for 2 hours. Furthermore, a platinum wire was wound around the side surface of this electrolyte layer to serve as a reference electrode. Pt mesh was used as a current collector.

[Evaluation of charge transfer resistance value and ohmic resistance value]
Subsequently, the charge transfer resistance value and ohmic resistance value of the fired composition were measured by an AC impedance method. The measurement temperature was 800° C., and the measurement frequency was 1 MHz to 0.01 Hz. Further, dry air was passed through the air electrode, and 3% H ₂ O-97% H ₂ was passed through the fuel electrode.

[Evaluation criteria]
The charge transfer resistance value was compared and evaluated with the measured value of Comparative Example 41. Comparative Example 41 is a particle composition consisting of a mixed powder of nickel oxide particles with a median diameter of 1 μm and yttria-stabilized zirconia particles with a median diameter of 3 μm, and is an evaluation sample of the prior art. Compared to the measured value of Comparative Example 41 , which is the conventional technology, ★ means 80% or less, ◎ means 85% or less, ○ means 90% or less, and × means more than 90%. I decided that. The ohmic resistance value is ★ if it is 80% or less compared to the measured value of Comparative Example 41 , ◎ if it is 85% or less, ○ if it is 90% or less, and ○ if it is more than 90%. It was judged as ×. The evaluation results are shown in Table 2-5m and Table 2-6.

[Measurement of median diameter]
An appropriate amount of the composition was taken and heated on a hot plate at 200°C to dry the solvent, thereby obtaining a dry composition. The dried composition was embedded in an epoxy resin, and the cross section was extracted by cross-sectional polishing and FIB processing. Cross-sectional TEM observation of this sample was performed, and TEM observation of a 10 μm square area was performed. A field emission transmission electron microscope JEM-2100F (manufactured by JEOL Ltd.) was used for TEM, and a JED-2300T (manufactured by JEOL Ltd.) was used for EDS. Using TEM-EDS, it was determined whether each particle was nickel or an ion-conductive ceramic particle. A TEM image was taken and used for particle size measurement. The particle diameter was measured using image analysis software Image Pro Premier 9.2 (manufactured by Media Cybernetics). As a specific procedure for analyzing the particle size, the brightness, contrast, and gamma value of the image are adjusted, and then calibration data is created using the scale bar of the TEM. Set "area" as the measurement item and use the division command to detect particle boundaries. A count command was executed to determine the area of the particles, particle diameter=circle equivalent diameter=2×√(area÷pi), and the median diameter of the particles (ie, D50 value) was determined from this data. At this time, measurement values in which the particle area was 1 pixel x 1 pixel or less were judged to impair the accuracy of the measurement since this is the smallest unit of the number of pixels in a TEM image, and were excluded from the analysis. Also, using the equivalent circle diameter of each particle obtained here, calculate the volume of the particle = 4 ÷ 3 × pi × (equivalent circle diameter ÷ 2) ³ , and calculate the particle volume for each of particles (A) to (D). The volume content of each of particles (A) to (D) was calculated by taking the total, and the ratio of the volume content of particles (A) to (D) was determined.

The median diameters of the particles (A), the particles (B), the particles (C), and the particles (D) were as shown in Table 2-1 and Table 2-2.

[Volume ratio of nickel element and ion conductive ceramics]
The dried composition was subjected to ICP emission spectroscopy analysis according to the following procedure, and the volume ratio of nickel element to yttria-stabilized zirconia was calculated. First, the dried composition was dissolved in an acid solution and subjected to ICP emission spectroscopy. From the obtained measured values, the weight ratio of nickel element to yttria-stabilized zirconia was calculated. By converting this value into a volume ratio using each solid density (8.9 g/cm ³ for nickel and 6.0 g/cm ³ for yttria-stabilized zirconia), the volume ratio of nickel element to yttria-stabilized zirconia is determined. was calculated. Using a similar method, the volume ratio of nickel element to scandia-stabilized zirconia was calculated. The results are shown in the columns of "nickel element content" and "ion conductive ceramic content" in Tables 2-3 and 2-4.

[Content ratio of mixed powder in composition]
Take an appropriate amount of the composition and heat it to 800°C at 5°C/min and nitrogen flow (200ml/min) using a TG-DTA device (manufactured by Hitachi High-Tech Science, trade name: TG/DTA7220) to remove the solvent. All was removed by volatilization. The content ratio of the mixed powder was calculated from the weight change in this step.

[Evaluation of workability]
In the above "evaluation sample production process", the composition was coated on the yttria-stabilized zirconia substrate 10 times, and the case where a normal coating film was produced 9 times or more (yield 90% or more) was judged as ○. . A case where a normal coating film was obtained less than 9 times (yield less than 90%) due to an abnormality such as cracking of the coating film or collapse of the film shape was evaluated as Δ. The evaluation results are shown in Tables 2-5 and 2-6.

Examples according to the present invention are 41 to 78, examples containing particles (C) are 50 to 52, 54, 56 to 76, and examples containing particles (D) are 52 to 74, 77, 78. It is. Among the Examples containing particles (C) and (D), Examples 56 to 74 satisfy the relationship of volume content of particle (A) > volume content of particle (C), and The following relationship is satisfied: volume content of particles (B)>volume content of particles (D). Preferred examples of particle compositions according to the invention are 41, 44-56, 59-65, 68-70, 73, 74. Comparative Examples 41 to 53 show results in cases where the requirements for the particle composition according to the present invention were not satisfied.

The mixed powders of Examples 41 to 78 according to the present invention are made of metallic nickel particles (A) having a median diameter of 10 nm or more and 200 nm or less, and ion conductive ceramic particles (B) having a median diameter of 10 nm or more and 200 nm or less. The conventional technology does not meet these requirements because the ratio of the volume of nickel element to the volume of oxide constituting the ion-conductive ceramic particles is within the range of 20/80 to 80/20. In comparison with Comparative Example 41, it was confirmed that both high catalytic activity and high conductivity were achieved.

Further, in Examples 50 to 52, 54, and 56 to 74 containing nickel-containing particles (C) having a median diameter of 300 nm or more and 10 μm or less, it was confirmed that the conductivity was further improved. Furthermore, it was confirmed that Examples 52 to 74, which were characterized by containing ion-conductive ceramic particles (D) having a median diameter of 300 nm or more and 10 μm or less, had increased conductivity. Further, the volume content of the metal nickel particles (A) is greater than the volume content of the nickel-containing particles (C), and the volume content of the particles (B) is greater than the volume content of the particles (D). In Examples 51 and 55 to 74, it was confirmed that the charge transfer resistance value was reduced.

In addition, Examples 41 to 78 all meet the requirements of the present invention and have both excellent catalytic activity and high conductivity, but in particular, the content ratio of the mixed powder in the composition is 20% by weight or more and 95% by weight. % or less, Examples 41, 44 to 56, 59 to 65, 68 to 70, 73 to 78 have a mixed powder content ratio of less than 20% by weight or more than 95% by weight in Example 42. , 57, 58, 66, 67, 71, and 72, it was confirmed that it was possible to achieve even higher workability at the same time.

From the above examples, the present invention can be used to improve the catalytic activity and conductivity, which are important characteristics required for electrode materials and catalysts, and to improve the efficiency of functional materials. For example, it has been shown that it can be used in the fuel electrode of SOFC, the cathode of SOEC, and the fuel electrode of proton conduction fuel cells to reduce internal resistance, and can be used as a catalyst to improve reaction efficiency.

The mixed powder of the present invention has high catalytic activity due to the use of fine particles and excellent conductivity due to the use of metal nickel, and is suitable for use in solid oxide fuel cells (SOFCs) and proton conduction fuel cells. It can be used in a wide range of applications, such as cathodes of solid electrolyte water electrolysis cells (SOEC), and reforming catalysts for hydrocarbon compounds such as natural gas.

Claims (5)

Metal nickel particles (A) having a median diameter of 10 nm or more and 200 nm or less,
Ion-conductive ceramic particles (B) having a median diameter of 10 nm or more and 200 nm or less,
A nickel-ion conductive ceramic mixed powder containing
The content of nickel element contained in the nickel-ion conductive ceramic mixed powder and the content of ion conductive ceramic particles are in a volume ratio of [nickel element]/[ion conductive ceramic particles] = 20/80. ~80/20,
Nickel-ion conductive ceramic mixed powder used as electrode material or catalyst . The nickel-ion conductive ceramic mixed powder used for the electrode material or catalyst according to claim 1, further comprising nickel-containing particles (C) having a median diameter of 300 nm or more and 10 μm or less. The nickel-ion conductive ceramic mixed powder for use in an electrode material or catalyst according to claim 1 or 2, further comprising ion conductive ceramic particles (D) having a median diameter of 300 nm or more and 10 μm or less. The content volume of the metal nickel particles (A) and the nickel-containing particles (C) satisfy the relationship of volume content of the particles (A)>volume content of the particles (C), and the ionic conductivity According to claim 2 or 3, the content volume of the ceramic particles (B) and the ion conductive ceramic particles (D) satisfies the relationship: volume content of the particles (B)>volume content of the particles (D). Nickel-ion conductive ceramic mixed powder used for the electrode material or catalyst described above. A particle composition for use in an electrode material or catalyst, comprising 20% by weight or more and 95% by weight or less of the mixed powder according to any one of claims 1 to 4, and further comprising a solvent.