JP7076788B2 - Anodic material for solid oxide fuel cell and its manufacturing method, and solid oxide fuel cell - Google Patents

Description

The present invention relates to an anode material for a solid oxide fuel cell and a method for manufacturing the same, and more particularly to an anode material for a solid oxide fuel cell and a method for manufacturing the same, which significantly improves the power generation efficiency of the entire system of the solid oxide fuel cell. The present invention also relates to a solid oxide fuel cell using this anode material.

Solid oxide fuel cells have the highest power generation efficiency among fuel cells, and in addition to the large-scale fuel cells that have been studied in the past, when high efficiency and high performance can be achieved, the size of the battery will be significantly reduced. As fuel cells can be used in apartment buildings, efforts are underway to further improve power generation efficiency.

One of the major goals of research and development of fuel cells is to improve power generation efficiency, which is also a big issue for solid oxide fuel cells. In a fuel cell, the oxygen reduction reaction (reaction that creates oxide ions from oxygen gas and takes them into a solid electrolyte) performed on the cathode (oxygen electrode) side is the hydrogen oxidation reaction (creating protons and oxidizing) that occurs on the anode (fuel electrode) side. Since it is extremely slow compared to the reaction that reacts with physical ions to form water molecules as a result (also called water molecule formation reaction or fuel cell anode reaction), it is possible to promptly carry out this reaction by improving the cathode, which is the power generation efficiency. It has been a common understanding of those skilled in the art for many years that the improvement of the performance on the anode side is far less important and less effective than the improvement of the performance of the cathode. In the study of solid oxide fuel cells, improvement of the anode side has also been proposed (for example, Non-Patent Document 1). However, in order to promote the spread of oxide fuel cells, the anode support is being researched and developed to lower the operating temperature and enable the use of metal as an interconnector material (650 ° C to 750 ° C). In the development of a thin film oxide fuel cell, it has not been achieved to reduce the excessive overvoltage existing in the resistance in the anode layer at the above temperature to improve its characteristics.

The operating temperature of solid oxide fuel cells, for which research and development has been promoted, is about 1000 ° C. However, in a relatively low temperature region of 800 ° C or lower, the power generation efficiency drops significantly due to an increase in internal resistance, etc. Practically, it has been considered necessary to operate at 900 ° C. or higher. However, the materials that can be used are limited at high temperatures of 900 ° C or higher, and lanthanum is a material for interconnectors that becomes the limit between single cells, especially when stacking single cells to create a stack cell to obtain high output. Chromite-based oxides are mainly used. However, interconnectors using this material are very expensive, which is one of the major factors that hinder the price reduction of solid oxide fuel cells. If the operating temperature of a solid oxide fuel cell can be lowered to about 650 ° C to 750 ° C, general-purpose stainless steel can be used as an interconnector material, and it is expected that the fuel cell price can be significantly reduced. There is.

For that purpose, it is considered effective to reduce the thickness of the solid electrolyte to 20 microns or less to significantly reduce the internal resistance. However, when the solid electrolyte membrane is made of ceramics, it is a support that supports the membrane. Since it is not possible to form a self-supporting film without a solid material, it has been attempted to form a ceramic film on a support using an inexpensive anode material instead of an expensive cathode material.

However, the anode material usually consists of a mixture of Ni particles and oxide solid electrolyte particles. In this case, Ni particles are linked to transport electrons, and oxide solid electrolyte particles (eg, yttria-stabilized zirconia particles, Scandia-stabilized zirconia particles, ceria particles, etc.) are linked to diffuse oxide ions. It has a role as a passage to make it. When hydrogen gas comes into contact with the contact points of these two different particles, three types of hydrogen, electrons, and oxide ions meet at the same time, and the fuel cell reaction proceeds (this is called the three-phase interface, which is the active site in the anode. It is believed to have a role).

However, in order to greatly increase the number of active sites, a method such as reducing the particle size can be considered, but in order to suppress the abnormal grain growth of Ni in the anode layer and exert high Ni activity, it is possible to exert high Ni activity. Usually, Ni oxide is used instead of Ni, and by reducing this at a temperature of 800 ° C., an anode layer composed of the above-mentioned mixture of Ni particles and solid oxide electrolyte particles is formed.

Furthermore, when the anode layer is baked onto ceramics, the baking process is usually performed at a temperature exceeding 1000 ° C., so the particle size of the Ni particles and the oxide solid electrolyte particles in the anode layer is fine only to about submicron. In addition, when the above-mentioned three-phase interface is formed, an oxide layer in which the Ni surface is partially oxidized is formed, especially at the interface between Ni and stabilized zirconia, so that the anode reaction occurs. It was difficult to dramatically improve the number of active sites compared to those in the conventional anode layer, and to reflect the improvement effect in the power generation efficiency.

Due to the significant decrease in power generation efficiency during low temperature operation and the difficulty of solving it, the prospects for practical use of solid oxide fuel cells showing high power generation efficiency at temperatures of 800 ° C or lower have been clear until recently. There wasn't.

The inventor of the present application has proceeded with research to solve this problem by forming a platinum oxide film on a layer of a mixture of zirconia or ceria powder and nickel oxide powder by sputtering or the like and heating it in a hydrogen atmosphere. An attempt was made to use the obtained material as an anode material for a solid oxide fuel cell. In the first place, as described above, it was considered that the performance improvement on the anode side hardly contributes to the performance of the fuel cell using the anode side in the conventional technical wisdom. Although the amount of platinum used was extremely small in view of conventional wisdom, it was found that the high power generation efficiency was maintained at 700 ° C, which is a very low operating temperature range compared to the conventional method (). Patent Document 1).

However, the anode material shown in Patent Document 1 contains a specific metal called platinum as an essential component. Shirokane is not only expensive, but also has a very low output, and the production areas are extremely unevenly distributed. Therefore, the price and supply are demand, speculation, and even production due to the expansion of future fields of use. There is a high possibility that it will become unstable in the short and long term due to the influence of the political situation of departure. Therefore, it is strongly desired to develop a material having characteristics similar to those of the anode material disclosed in Patent Document 1 even if platinum is not used at all or the amount of platinum used is further reduced.

The subject of the present invention is an anode material capable of greatly improving the power generation efficiency of the solid oxide fuel cell as a whole even if the amount of platinum used is reduced by not using platinum or by using it in combination with other substances. Is to provide.

According to one aspect of the invention, one or more metal elements (with zirconia or ceria, nickel and divalent cations having an ionic radius within ± 10% of the ionic radius of the divalent cation of platinum). However, an anode material for a solid oxide fuel cell is provided, which comprises (except when the metal element is platinum alone) and has a composition ratio of the metal element in the range of 4 to 400 ppm.
Alternatively, one or more metal elements whose ionic radius is within ± 10% of the ionic radius of the divalent cation of platinum when zirconia or ceria, nickel and divalent cations are used (however, the metal element is platinum). The metal element is provided as an anode material for a solid oxide fuel cell, which does not exist at the interface between zirconia or ceria and nickel as particles having a diameter of 1 nm or more.
Alternatively, one or more metal elements whose ionic radius is within ± 10% of the ionic radius of the divalent cation of platinum when zirconia or ceria, nickel and divalent cations are used (however, the metal element is platinum). The metal element is in the form of a defect association cluster in which the cations and nickel defects of the metal element and the oxygen defects created to balance these cation defects and charges are combined. Given the anode material of the solid oxide fuel cell.
Here, it may function as an anode of a solid oxide fuel cell at 700 ° C.
Further, the metal element may be one or a plurality of types selected from the group consisting of rhodium, ruthenium, palladium, iron and zinc, or the selected one or a plurality of types to which platinum is further added. ..
Alternatively, the metal element may be manganese or manganese with platinum added.
Here, the metal element may be further selected from the group consisting of rhodium, ruthenium, palladium, iron and zinc.
It may also have a porous structure.
Further, the zirconia may be yttria-stabilized zirconia.
According to another aspect of the present invention, an oxide film of the metal element is formed on a layer of a mixture of a powder of zirconia or ceria and a powder of nickel oxide, and the oxide film is formed on the mixture. The layer is heated in a hydrogen atmosphere of pure hydrogen or dilute hydrogen to diffuse the metal element cation from the oxide film into the layer and reduce nickel oxide in the layer. A method for manufacturing an anode material for a solid oxide fuel cell is provided.
Here, at least a part of the particles constituting the zirconia or ceria powder may be nanowires.
Further, a porous structure may be formed in the layer by heating the mixture in the hydrogen atmosphere.
Further, the layer of the mixture may be formed from a slurry of zirconia or ceria powder and nickel oxide powder.
Further, after the formation of the layer of the mixture, a baking treatment may be performed.
Further, the oxide film may be formed by sputtering.
According to still another aspect of the present invention, a solid oxide fuel cell having an anode using any of the anode materials is provided.

According to the present invention, in Patent Document 1, instead of platinum as the metal element used for the anode material, or when rhodium (Rh), palladium (Pd) or ruthenium (Ru) is used together with platinum, further. Even if other elements whose ionic radius is similar to that of Pt ²⁺ are used when they are divalent cations, they exhibit characteristics similar to those when platinum is used, and they are used as anode electrodes. The power generation efficiency of the solid oxide fuel cell used in the above can be remarkably improved. This makes it possible to provide an anode electrode that contributes to the realization of a solid oxide fuel cell having improved power generation efficiency as compared with the conventional case, without using platinum or while suppressing the amount of platinum used. In addition, due to this efficiency improvement, even if the solid oxide fuel cell is operated at about 650 ° C to 750 ° C, where a metal can be used instead of the lantern chromite-based oxide as the material for the interconnector, the power generation efficiency is higher than before. Therefore, it is possible to reduce the manufacturing cost by increasing the choice of materials that can be used due to the low temperature operation, and to realize the use of the fuel cell in the apartment house by improving the high efficiency power generation performance.

The figure explaining the Rh cation-defect oxide-Ni cation cluster active site in the anode catalyst of this invention in comparison with the three-phase surfactant active site of the prior art. The figure explaining the method of obtaining IR-free by the current cutoff method. Graph for estimating ionic radius of Ru ²⁺ and Rh ²⁺ . Rh ³⁺ (assumed to be represented by Rh ²⁺ ), Fe ³⁺ (represented by Fe ²⁺ having the largest ionic radius among possible valences), Mn ⁴⁺ (represented by Fe 2+) on the Ni surface in the anode material of the present invention. The principle diagram explaining that the interface structure formed by (assumed to be represented by Mn ²⁺ ) is useful for promoting the anodic reaction of the fuel cell. Rh ³⁺ (assumed to be represented by Rh ²⁺ ), Fe ³⁺ (represented by Fe ²⁺ having the largest ionic radius among possible valences), Mn ⁴⁺ (represented by Fe 2+) on the Ni surface in the anode material of the present invention. A principle diagram explaining that the interface structure formed by Mn ²⁺ , which has the largest ionic radius among the valences that can exist), is useful for promoting the anodic reaction of the fuel cell. The figure for demonstrating the surface unit cell of NiO shown on the right side of FIG. 5A in more detail. The interface structure formed by Rh ³⁺ (assumed to be represented by Rh ²⁺ ), Fe ³⁺ (assumed to be represented by Fe ²⁺ ), and Mn ⁴⁺ (assumed to be represented by Mn ²⁺ ) on the Ni surface in the anode material of the present invention is a fuel cell. The principle diagram explaining that it is useful for accelerating the anodic reaction. In the present invention, it is a figure for demonstrating that ceria can be used instead of zirconia as an oxide electrolyte, and the left side shows the size of NiO, and the right side shows the size of the surface unit cell of cubic zirconia. In the present invention, it is a figure for demonstrating that ceria can be used instead of zirconia as an oxide electrolyte, and shows the size of the surface unit cell of ceria. A graph showing the net cell voltage (IR-free) characteristics of a solid oxide fuel cell containing Rh in the anode material of the embodiment of the present invention, corrected for the influence of the current density at an operating temperature of 650 ° C. and the internal resistance of the battery. .. Here, the sputtering thickness of the RhOx thin film in the process of producing the anode layer was set to 1 nm, 5 nm, and 10 nm (plots with ◯, Δ, and ▽, respectively). In addition, a comparative example (without RhOx film) was plotted with □. The figure which shows the result of having measured under the same conditions as FIG. 12 except that the operating temperature of a solid oxide fuel cell was set to 700 degreeC. The graph which shows the net cell voltage (IR-free) characteristic at the operating temperature of 650 ° C. in the solid oxide fuel cell which contains Pd in the anode material of the Example of this invention. Here, the sputtering thickness of the PdOx thin film in the process of producing the anode layer was set to 1 nm and 10 nm (plots with ◯ and ▽, respectively). In addition, a comparative example (without PdOx film) was plotted with □. The figure which shows the result of having measured under the same conditions as FIG. 12 except that the operating temperature of a solid oxide fuel cell was set to 700 degreeC. The graph which shows the net cell voltage (IR free) characteristic at the operating temperature 650 ° C. in the solid oxide fuel cell which contains Ru in the anode material of the Example of this invention. Here, the sputtering thickness of the RuOx thin film in the process of producing the anode layer was set to 1 nm, 5 nm, and 10 nm (plots with ◯, Δ, and ▽, respectively). In addition, a comparative example (without RuOx film) was plotted with □. The figure which shows the result of having measured under the same conditions as FIG. 14 except that the operating temperature of a solid oxide fuel cell was set to 700 degreeC. The graph which shows the net cell voltage (IR-free) characteristic at the operating temperature 700 degreeC in the solid oxide fuel cell which contains Fe in the anode material of the Example of this invention. Here, the sputtering thickness of the FeOx thin film in the process of producing the anode layer was set to 1 nm and 10 nm (plots with ◯ and □, respectively). In addition, a comparative example (without FeOx film) was plotted with Δ. The graph which shows the net cell voltage (IR-free) characteristic at the operating temperature of 700 degreeC in the solid oxide fuel cell which contains Mn in the anode material of the Example of this invention. Here, the sputtering thickness of the RuOx thin film in the process of producing the anode layer was set to 1 nm. The figure which shows the result of having measured under the same conditions as FIG. 17 except that the sputter thickness of a RuOx thin film was set to 10 nm.

According to one embodiment of the present invention, an anode in which rhodium (Rh), palladium (Pd) or ruthenium (Ru) is added in place of platinum (Pt) in Patent Document 1 or together with Pt in addition to nickel (Ni). By using the material, characteristics similar to those in the case of Patent Document 1 are exhibited, and the efficiency of the solid oxide fuel cell is greatly improved. In particular, when Rh is used, a solid oxide fuel cell having higher performance can be obtained as compared with the case where Pt is used. More generally, an element having an ionic radius of about the same as the ionic radius of Pt ²⁺ (specifically, within ± 10% of the ionic radius of Pt ²⁺ ) when a divalent cation is used can be used. .. In the following general explanation, Rh is basically taken as an example, but unless otherwise specified, such explanation is about the ionic radius of Pd, Ru, Fe, Zn, etc. It should be noted that this holds even when an element that satisfies the above conditions is used. Further, although yttria-stabilized zirconia is used as the solid electrolyte in the following description, other materials used in the technical field of the present invention, for example, ceria, can also be used.

More specifically, the anode materials of the present invention are, for example, zirconia (ZrO ₂ ) (preferably yttria-stabilized zirconia (YSZ)) and nickel oxide (NiOx, where 1 ≦ x ≦ 4, below. The same applies. In the following, NiOx may be abbreviated as NiO) on a very thin layer of rhodium oxide (RhOx, where 0.5 ≦ x ≦ 2, and the range of this x is for elements other than Rh. The same applies in this case) is formed on a solid oxide (for example, YSZ) as an electrolyte, and this is formed in a reducing atmosphere containing hydrogen (diluted hydrogen diluted with helium or the like as in the examples, or pure hydrogen. It may be produced by heating in (may be). A layer of a mixture of YSZ and NiOx (YSZ-NiO) is heated in a reducing atmosphere in a state where the RhOx film is not formed, and NiO in the layer is reduced to Ni to reduce the porous anode to a solid oxide. It has been conventionally known to form on an electrolyte. However, in solid oxide fuel cells, it has been recognized that the use of Pt, which is the same platinum group element as Rh, in the anode layer is not very effective, and RhOx is used in such a form. There was no example of making an anode material.

In the anode material of the present invention, as can be understood from the peculiar microstructure described later, as in the case of Pt described in Patent Document 1, the amount of Rh occupying the entire anode material is determined by another type using Rh. The catalytic activity is maintained at a high value even if it is significantly reduced as compared with the electrode material of the fuel cell. In the examples described below, the amount of Rh in the anode material ranges from 65 mg / kg (= ppm) to 6.5 mg / kg (= ppm) (the thickness of the RhOx formed in the examples is 10 nm to 1 nm). Although it was changed, even in the case of an extremely small amount of 6.5 mg / kg (= ppm), there was no sign of a significant decrease in the power generation performance of the fuel cell, which would be a practical obstacle. Therefore, the lower limit of the Rh amount specifically demonstrated in the examples is 6.5 mg / kg (= ppm), but the anode material of the present invention exhibits sufficiently high performance even with a smaller Rh amount. Conceivable. The amount of Rh in the anode layer was confirmed by quantitative analysis by inductively coupled plasma mass spectrometry (ICP-MS) (device used: PerkinElmer ELAN DRCII ICP-MS).

Here, the active sites formed in the anode material of the present invention will be described in comparison with the active sites in the conventional anode material.

As described above, conventionally, the anode electrode reaction of a fuel cell is considered to occur at a site where electrons-gas (hydrogen) -ions (oxide ions) meet, that is, a site called a three-phase interface, and these three phases occur. The position where the interface is formed is the contact portion between the oxide that becomes the electrolyte and the electrode active material (Ni in the anode material of the conventional structure mentioned as a comparative example in the examples). FIG. 1 (a) conceptually shows the structure of a conventional anode without a RhOx thin film, i.e., where the conventional three-phase interface acts as an active site. The left side of FIG. 1A shows a state in which a layer of a mixture of oxide electrolyte particles and NiOx particles is formed on the surface of a solid electrolyte. The right side conceptually shows the structure of the anode material after the reduction treatment at 800 ° C. in the hydrogen atmosphere of the one on the left side. By this treatment, NiOx is reduced to metallic Ni. At this time, since the volume is reduced, a large number of pores are formed in the composite material of the oxide electrolyte and Ni after reduction, so that the composite material becomes porous. In this porosity, a conventional three-phase interface is formed at the interface between Ni and the oxide electrolyte, and this becomes an active site (indicated by a blank cross on the right side of FIG. 1A).

If the active site of the anode material of the present invention can also be explained by the above-mentioned conventional three-phase interface model, since the presence of Rh is important in the anode material of the present invention, it is natural for the three-phase interface that functions as the active site. Fine particles of Rh should be present (because they are initially introduced into the anode in the form of oxide RhOx, but subsequent reduction treatment in a hydrogen atmosphere should reduce not only NiOx but also RhOx). When Pt is used as a component of the electrode of a fuel cell, the Pt particles existing at the three-phase interface in the Pt particle are at least several nm, as is well known, referring to the observation results of the electrode of the polymer electrolyte fuel cell, for example. It exists in the form of fine particles of the diameter of. Further, as an anode material containing Pt for a solid oxide fuel cell, for example, there is one disclosed in Non-Patent Document 1 already mentioned, but also in Non-Patent Document 1, heat treatment is performed at a temperature of about 900 ° C. It is shown that Pt in the anode material is a particle having a diameter of about 50 nm or more and about 100 nm. For details, refer to Non-Patent Document 2 published together with the supplementary information of Non-Patent Document 1. B of Figure S6 of Non-Patent Document 2 shows a TEM image of a three-phase interface at a portion where SDC (samaria-doped-ceria) and Pt are in contact, and a part thereof is visible in the upper left. It can be seen that the Pt particles have a diameter of at least 50 nm or more and about 100 nm after being heat-treated at a temperature of about 900 ° C. Further, the white, clearly shining platinum particles designated as Pt in F of Figure S1 of the same document are considered to be particles after heat treatment at 900 ° C. with reference to the caption in FIG. D. It is considered that almost the same result is obtained even when Rh is used instead of Pt.

In known documents, for example, Non-Patent Document 3 is an example of using a precious metal such as Pt or Rh in a small amount (several wt%) in the anode layer for an oxide fuel cell. However, in the case of this document, the anode uses Ni-SDC instead of Ni-8YSZ. That is, as in Non-Patent Document 2 referred to in Patent Document 1, SDC of a mixed conductor is used instead of 8YSZ. However, even when the above-mentioned anode material introduced in Non-Patent Document 3 is used, sufficient performance cannot be exhibited at 800 ° C. or lower. It is considered that the limit in the case of a system in which a small amount of particles are added is near this temperature. Further, when a mixed conductor is used instead of YSZ in this way, Ce ⁴⁺ in the mixed conductor (SDC, etc.) is reduced to Ce ³⁺ , and at that time, the ionic radius of Ce ³⁺ is large. Large strain occurs at the three-phase interface due to large volume expansion. It is not preferable to use a mixed conductor here because it causes a decrease in performance, a decrease in stability, and a decrease in the number of functioning three-phase interfaces.

Therefore, assuming that the three-phase interface in the present invention has essentially the same structure as the conventional one, at least several nm is formed at the place where the three-phase interface serving as the active site is formed in the embodiment of the present invention. Fine particles of Rh with a diameter of should be observed.

However, even when compared with the case of Non-Patent Document 3 referred to above, the precious metal is used in an extremely large amount of several wt% as compared with the present invention. On the other hand, as can be seen from the examples shown below, since the anode material of the present invention exhibits high activity, it is necessary to consider that there are an extremely large number of active sites thereof. Therefore, if each active site requires fine particles of Rh of several nm to obtain its activity, the anode material of the present invention containing only a very small amount of Rh will achieve such high activity. It will not be possible to provide a very large number of Rh fine particles for this purpose. After all, as in the case of Patent Document 1, also in the anode material of the present invention, the interface between the oxide electrolyte particles and the Ni particles, which should form a three-phase interface functioning as an active site, is about 1 nm or more. It must be assumed that there are no large Ru particles.

Since this anode material is extremely active compared to the conventional anode material that does not use RhOx, considering that a large number of active sites should naturally exist on it, the result of the above consideration is the conventional three. It is suggested that there must be an active site there, which is a structure that cannot be explained by the phase interface model and is a new three-phase interface that is much smaller than when assuming a conventional three-phase interface structure. ing. More specifically, in the anode material using RhOx in the present invention, the element Pt used in Patent Document 1 for Rh in the present invention belongs to the same platinum group, and this anode material is described in Patent Document 1. It should be considered that a structure equivalent to the result of examining the anode material using PtOx in Patent Document 1 is formed in consideration of achieving almost the same action and effect as those of the above.

To reiterate the explanation in Patent Document 1 on this point, Pt is described in Non-Patent Document 4, which publishes research results on a new active site structure in a Pt-supported ceria electrode active material of a polymer electrolyte fuel cell. It has been shown that cations and cerium cations form clusters with very small atomic-level sizes, which are bonded through lattice defects in the ceria crystal, and that these clusters exhibit strong electrochemical catalysis. There is. In the anode material prepared in Patent Document 1, Pt particles having a diameter of about 1 nm or more are not observed at the interface between zirconia or ceria and nickel, and Pt is uniformly dispersed on the anode material without forming agglomerates. Considering that it has a very high activity, a large amount of cation-defect oxide clusters similar to those presented in Non-Patent Document 4 form a new three-phase interface on this anode. It is reasonable to judge that it is dispersed in. Therefore, even in the present invention in which Rh (or Pd, Ru) is used instead of Pt, a new three-phase interface equivalent to that clarified in Patent Document 1 is dispersed in a large amount in the anode material of the present invention. Can be thought of as being.

In the above description, an example was taken when Ru was used as an element to be added in a trace amount to the cluster, but as will be described later, more generally, it is a divalent element such as Fe ²⁺ and Zn ²⁺ . It should be noted that it is also applied when an element having an ionic radius of the same level as the ionic radius of Pt ²⁺ (specifically, within ± 10% of the ionic radius of Pt ²⁺ ) is used as a cation. ..

This is conceptually shown in FIG. 1 (b). The left side of FIG. 1B shows a state in which a 10 nm-thick RhOx thin film is formed on the surface (lower side in the figure) of an anode layer having a thickness of about 40 μm formed of a mixture of an oxide electrolyte and NiOx. .. In this state, when treated in a hydrogen atmosphere at 800 ° C. as in FIG. 1 (a), Rh cations diffuse from the RhOx thin film into the oxide electrolyte and the NiOx layer. Since NiOx remains in the layer of the mixture in the process of reduction treatment in a hydrogen atmosphere,
RhOx + Y ₂ O ₃ Stabilized ZrO ₂ + NiO →
The reaction of Rh cation-defective oxide-Ni cation cluster formation proceeds, and as a result, at the end of the reduction treatment, as shown on the right side of FIG. 1 (b), the above cluster (inside) is placed on the oxide electrolyte and metallic Ni. (Indicated by a blank star ☆) is densely and uniformly formed. To explain the above-mentioned "Rh cation-defect oxide-Ni cation cluster" in more detail, it is first known that this cluster is formed on the partially oxidized layer on the Ni surface. Therefore, using Pt used in the previous patent application (Patent Document 1) by the applicant of the present application as an example, surface defect structure simulation (modeling) was performed using the source code GULP, and the most appropriate defect association cluster was estimated. .. As a result, the constituent elements of the defect association cluster in this case are Ni defects (formal charge minus 2 values) and Pt ²⁺ defects (formal charge:) created by Pt ²⁺ entering the quasi-lattice position (Frenkel defect site) of the NiO lattice. Of course, +2 valence), oxygen defects (formal charge: +2 valence), and oxygen defects become lattice defects (formal charge: -2 valence) created by entering the quasi-lattice position (Frenkel defect site) of the NiO lattice, and the charge is neutral. It was obtained that the association defect was formed so as to be. That is, this is a defect association cluster in which Pt cations and Ni defects, and oxygen defects created to balance these cation defects and charges are combined. Since this result is consistent with the analysis result by the analysis electron microscope, it is considered to have sufficient validity. Here, instead of the Pt cation, the same result is obtained even when the ionic radius of the divalent cation is sufficiently close to the ionic radius of Pt ²⁺ (Rh, etc., exemplified below) as described below. Become. In the present application, the defect-association cluster having the structure described above is also referred to as a defect-association cluster or a more simplified cluster. Since this cluster is composed of only a few atoms, its size is at most a few Å. Therefore, these clusters cannot be detected at all even when observed with a spatial resolution of about 1 nm. For example, assuming a model in which clusters of rhodium cations, defective zirconia, and Ni cations exist in stabilized zirconia, it is assumed that the rhodium cations are Rh ³⁺ and the number of oxygen coordinated around them is 6. Then, since the ion radius of the rhodium cation (Rh ³⁺ ) is considered to be about 0.665 Å (0.0665 nm), it cannot be naturally seen with a spatial resolution of about 1 nm. However, it is possible to verify the existence of such a cluster. First, if such a cluster is present in the anode material, an oxide of Rh or Rh is naturally present there, and this can be confirmed as a metal or a metal oxide by observation with an analytical electron microscope. However, when such a metal exists in the form of an alloy with Ni, it is accompanied by expansion or contraction of the Ni lattice, but since the cluster is an aggregate of atoms, it is usual to change the lattice constant of Ni. Is unthinkable. Therefore, although it can be confirmed by observing an analytical electron microscope that Rh or Rh oxide is present in the anode material, the particles of Rh or Rh oxide cannot be confirmed by the electron microscope, and the anode material. If it can be confirmed that the lattice constant of Ni in the medium does not increase or decrease, it can be determined that the above-mentioned clusters are present in the anode material.

It should be noted here that, on the right side of FIG. 1 (a) conceptually showing the distribution of the active sites (three-phase interface) of the prior art, the active sites are formed only in the contact portion between the oxide electrolyte and Ni. On the other hand, on the right side of FIG. 1 (b), the active sites of the present invention are shown to be distributed everywhere on the surface of the anode material (including the surface inside the pores of the porous body). This will be described below.

In the process of research conducted by the inventor of the present application, when the inside of the anode layer was carefully observed by an analytical TEM, the oxide component moved to the Ni metal side, and the Ni cation diffused onto the oxide, and in that region. It was found that a defect association cluster structure composed of Ni and an oxide component was formed. For details, refer to Non-Patent Documents 5 and 6.

As shown in these non-patent documents, the width of the interface between Ni and the oxide is at most 10 nm, but the width in which both components diffuse over the grain boundaries to almost the same distance is the width of the grain boundaries. It reached a total of 100 nm, which is about 10 times. In addition, it was considered that a superstructure (meaning a structure different from the matrix) was formed in the diffusion region, in the words of non-patent documents. Considering based on the simulation of the defect structure by the inventor of the present application, this is also a cluster structure composed of cations and defect oxides, and is a C-type rare earth structure (the crystals constituting the matrix are stabilized zirconia or In the case of ceria, it has a fluorite-shaped crystal structure, but it is known that the C-type rare earth crystal phase can coexist thermodynamically with this fluorite crystal phase, that is, it can coexist in the same state diagram. It was considered to have a similar arrangement. As described above, the conventional wisdom is that the conventional three-phase interface exists only at the grain boundaries of Ni and oxide, and the number of active sites thereof is limited. However, on the other hand, there was also a cause of deterioration of the characteristics. In other words, the result was obtained to deny the conventional technical wisdom that Ni diffuses vigorously into the solid electrolyte membrane and creates an unfavorable state such as an electron conduction path in the solid electrolyte. ..

In the present invention, the defect association clusters are formed on a partially oxide layer on the Ni surface that reduces the activity of Ni. Since the formation of the defect-associated cluster (formation on the Ni oxide layer that impairs the activity) has an action of promoting the activity of Ni in turn, it is considered that a remarkable effect is observed in a small amount. In addition, since this defect association cluster was not observed on the side of zirconia or ceria in the observation results by the inventor of the present invention, the defect association cluster formed on the surface of the partially oxidized Ni metal in the anode is the action of the present invention.・ It can be said that it has an effect.

Further, if the essence of the present invention is in the cluster structure consisting of the cation and the defective oxide as described above, the inventor of the present application further determines whether or not an element can be used as a cation in the present invention. Rather than the type (that is, the element that becomes a cation that is one of the constituent elements of the cluster is not limited to the platinum group element), the ionic radius of the divalent cation is the same as the ionic radius of Pt ²⁺ . I got the idea that it is important to be a degree. For example, since it is known that the ionic radius of the divalent cation Fe ²⁺ of iron (Fe) is close to Pt ²⁺ , the characteristics of the sample obtained by depositing FeOx and then reducing it by the same method as PtOx are measured. As a result, an effect similar to that when the above-mentioned platinum group element was used was obtained (details are shown in Examples). Further, the ionic radius of the divalent cation Zn ²⁺ of zinc (Zn) is also close to Pt ²⁺ .

Here, in order to obtain an appropriate range of ionic radii, if the ionic radii of Pt, Fe, Zn, Pd, Ru, and Rh are compared,
-Pt ²⁺ ionic radius (assuming oxygen 6 coordination): 0.80 Å
-Fe ²⁺ ionic radius (assuming oxygen 6 coordination): 0.78 Å
-Zn ²⁺ ionic radius (assuming oxygen 6 coordination): 0.88 Å
-Pd ²⁺ ionic radius (assuming oxygen 6 coordination): 0.86 Å
Will be.

As for Ru and Rh, there is no report on the ionic radius of the divalent cation, so if we substitute the ionic radius of the trivalent cation, it will be as follows:
-Ru ³⁺ ionic radius (assuming oxygen 6 coordination): 0.68 Å
-Rh ³⁺ ionic radius (assuming oxygen 6 coordination): 0.67 Å

The ionic radii of Fe ²⁺ , Zn ²⁺ and Pd ²⁺ are sufficiently close to the ionic radii of Pt ²⁺ , specifically within the range of 0.72 to 0.88 Å, which is ± 10% of the ionic radii. However, in the case of trivalent Ru cations and Rh cations, the ionic radius becomes considerably small, and the ionic radius is out of the above range of ± 10%. Therefore, for these cations, the ionic radius in the case of divalent is estimated. If an atom has multiple valences, but the radius of the ion of one valence is unknown, the ionic radius and valence are almost linear if the radius of the ion of another valence is known. There is a method of estimating an unknown ionic radius as having a relationship. This estimation method is widely used by those skilled in the art and is recognized as valid. Below, the divalent ionic radii of Ru ²⁺ and Rh ²⁺ are obtained by this estimation method.

Since the ionic radii of Ru and Rh cations are known for trivalent to pentavalent, the ionic radii of divalent cations are extrapolated based on these known values, respectively. This is shown in the graph of FIG. Numerically, it is as shown in the table below (however, assuming oxygen 6 coordination).

From this, it was confirmed that even in the case of Ru and Rh, the ionic radius of the divalent cation was sufficiently close to the ionic radius of Pt ²⁺ and was within the range of ± 10%. Therefore, if the ionic radius of the divalent cation is within ± 10% of the ionic radius of Pt ²⁺ , it is considered that the element can be used as an element contained in the anode of the present invention.

As the ionic radius, Crystal Radii (CR) based on the ionic radius of F ⁻ 1.19 Å and effective Ionic Radii (IR) based on the ionic radius of O ^2- are usually used. (Non-Patent Document 9). To outline the general criteria for which one to use, first, in the crystal structure, both metals and oxides may have the same type of crystal structure (for example, Ni and NiO), but in this case, the crystal structure It is preferable to adopt CR as the ionic radius because the discussion focuses on the similarity of. On the other hand, IR is generally used when comparing oxides or when only oxides are the subject of discussion. In Non-Patent Document 9, CR is adopted as the ionic radius because it is discussed that active sites are formed in the reduction process in which NiO becomes Ni. However, in the present application, the interface between NiO and YSZ is used. IR is used for thinking.

In the present invention, by allowing the Rh cation to participate in the formation of the cation-oxide interface in the anode layer, which has conventionally played a role of deteriorating the anode characteristics, the above-mentioned long-distance movement of Ni and oxide is combined with the above-mentioned long-distance movement. It is considered that the number of new active sites (three-phase interface) was significantly improved for the first time by creating a cluster structure that improves the electrode performance in a wider range, and as a result, it contributed to the improvement of power generation performance.

As described above, in completing the invention of Patent Document 1, the inventor of the present application is not bound by the conventional stereotype that active sites are generated only in an extremely narrow place where Ni and oxides meet, and the above-mentioned experimental results. As a result of conducting research based on the above, it is possible to form a new cluster structure that is widespread on Ni and oxides, and in the past, even if it was used in the anode layer, it means from the viewpoint of improving fuel cell performance. It was found that extremely large activity can be realized by the addition of Pt, which was thought to be absent. In the present invention, further research is carried out based on the idea that the invention can be extended to other than Pt, and it is possible to remarkably improve the power generation performance by improving the anode layer using Rh or the like.

Since Non-Patent Document 1 exists as one of the few prior examples in which Pt is used as an anode material for a solid oxide fuel cell, the difference between the present invention and the description of the document will be described here. To be precise, there is no similar prior document for Ni—YSZ-based anodes. In Ni-SDC and the like, it has been shown that an addition effect of about several percent appears at 800 ° C. or higher, but the operating temperature range aimed at by the present invention is considerably lower than this.

First, it should be noted that Non-Patent Document 1 uses metallic Pt instead of PtOx, which is an oxide of Pt, when producing the anode. As will be described below, PtOx and NiOx are considered to increase the reaction activity with other particles when the oxide is reduced to the metal particles, and the reaction activity of Pt is improved by the reduction of PtOx to platinum. In addition to the effects, the effect of improving the reaction activity on the Ni surface by reducing NiOx to Ni, and the effect of improving the surface reaction activity of the oxide particles by generating oxygen defects on the surface of the oxide particles, NiOx and the oxide solid electrolyte particles work together. Combined with the bidirectional diffusion phenomenon that occurs over a wide area, it is considered that a new three-phase interface is formed widely and in large quantities in the anode layer. Here, if the treatment is performed at an excessively high temperature, the bonds between the Ni particles having increased reaction activity on the surface and the oxide particles having oxygen defects are broken, which is generated by the formation of new clusters over a wide area as described above. It is not preferable because it impairs the formation of the phase interface (the novel three-phase interface in the present invention will be described in detail later).

Based on this idea, when platinum particles are sputtered from the beginning, there is no reduction process from such oxides to metal particles, but the grain growth and sintering of platinum particles due to the addition of heat treatment at a high temperature of 800 ° C. Therefore, the reaction activity with other particles does not increase sufficiently, and only a certain effect can be expected. Therefore, in order to increase the effect of improving anode performance to the measurable range, it becomes necessary to sputter a large amount of platinum, creating a state of low industrial utility value in which platinum, which is a rare metal, is heavily used. It ends up. Such a situation is considered to be the same even when rhodium or the like is used as the anode material instead of platinum.

Further, to further explain the usage of Pt in Non-Patent Document 1, although metal Pt is given by sputtering in Non-Patent Document 1, the film thickness thereof is a number as compared with 1 nm to 10 nm in the examples of the present application described later. The range is from 150 nm to 200 nm, which is ten times larger (the left column on page 160 of Non-Patent Document 1, the second paragraph of the "Method" section). Furthermore, it should be noted that the film in the examples of the present application is RhOx instead of metal Rh, and is thinner when converted to metal Rh. In fact, as already described, as a result of quantitative analysis of the anode of the embodiment of the present application, the content of Rh is in the ppm level from 6.5 mg / kg (= ppm) to 65 mg / kg (= ppm), which has already been reported. It was a very small amount compared to the% level of. That is, in Non-Patent Document 1, it is confirmed that the electrode performance is improved by using a much larger amount of Pt as compared with the present invention. On the other hand, in the examples of the present application, although only a small amount of Rh, which is about a few tenths of the amount, is used, a large improvement effect on the battery performance can be observed, and the Rh in the present invention can be observed. It can be understood that the utilization efficiency of is high.

If the three-phase interface is described here, the three-phase interface includes an electron (a phase responsible for charge transfer, a path in which Ni particles are conventionally connected), a gas phase (hydrogen in the anode layer), and an ion (). It refers to the interface where the phase responsible for the diffusion of oxide ions, which is conventionally the path in which oxide particles are connected, is concentrated in one place. In the case of the present application, in addition to the conventional three-phase interface, rhodium nanoparticles that are considered to be below the detection limit of high-resolution SEM are formed by the reduction of rhodium oxide, and oxygen is formed on the surface instead of simply causing grain growth. Combined with the bidirectional diffusion phenomenon that occurs between the oxide particles with defects and the Ni particles whose surface reaction activity has increased due to reduction, the three-phase interface that appears as the novel highly active active site described above is spread over a wide area. I was able to form it. As a result, it is considered that the fuel cell power generation performance can be improved.

Here, the bidirectional diffusion described above and the three-phase interface formed other than the contact point between the Ni particles and the oxide particles will be described.

Non-Patent Document 7 discloses a Pt-CeO ₂ / C electrode material obtained by impregnating ceria nanowires with Pt and mixing it with carbon black. Figure 3 shows an example of the result of TEM observation of the diffusion phenomenon from oxide particles (here, ceria) on metallic platinum, and Figure 12 shows an illustration of this diffusion phenomenon. It is shown. Although Pt is used as a metal in Non-Patent Document 7, it is considered that the same phenomenon occurs in Ni. As can be seen from these figures, the oxide particle component diffuses onto the metal particles in the form of a film having a thickness of several nm from the oxide particles. This diffusion proceeds while forming an interface structure (cluster structure). On the other hand, regarding the diffusion of the metal to the oxide particle side, in the Pt-CeOx nanowire electrode, the metal component diffuses to a slightly deeper range (which is considered to be about 10 nm) from the surface of the oxide particle. Further, as described above with reference to Non-Patent Documents 5 and 6, diffusion at equal distances from both sides is observed in the anode layer for the solid oxide type fuel cell, so that the Ni metal is oxidized. Diffusion of an object in a thin film state, and on the oxide side, metal components diffuse from the surface to the inside (depth direction) and along the surface, but defect clusters in either direction. Diffusion proceeds while forming a structure. When platinum is added, this diffusion range is considered to be widened. The same phenomenon occurs when rhodium or the like is used instead of platinum. Therefore, in both Ni particles and oxide particles, Rh cation-defective oxide-Ni cation clusters are formed everywhere as the diffusion progresses.

Further, although the metal Ni particles are connected to each other, the surface thereof is partially covered with an oxide component thin film. Since this oxide thin film naturally has an oxygen defect structure, it can be a route for carrying oxide ions. As for electrons, of course, they can move in Ni with low resistance and can encounter oxide thin films at various parts of the surface of the entire Ni particles. Also, since this thin film should take the form of non-uniformly (in other words, partially) covering the surface of the Ni metal particles, the number of three-phase interfaces encountered by the three parties of gas, electrons and ions on the surface of the Ni metal particles is The number is greatly increased as compared with the case where only the contact point between the Ni particle and the oxide particle is the three-phase interface. Further, in the anode material of the present invention, it is considered that a defect cluster structure that facilitates charge transfer, which is not found in the microstructure formed by the Pt cation, is made possible by the vapor deposition of RhOx.

In addition to this, considering the electron conduction path on the oxide particles, the metal component diffuses on the oxide particles side as described above. There are two types of this diffusion, one is diffusion from the surface to the inside and the other is diffusion along the surface. In any case, metal cations form clusters. That is, Rh ²⁺ sites and Ni ²⁺ sites are Zr ⁴⁺ and Y ³⁺ in the oxide crystal lattice (stabilized zirconia is a tetravalent and trivalent cation because Y ₂ O ₃ is dissolved in the ZrO ₂ lattice. Coexist) or Ce ⁴⁺ , Ce ³⁺ (Ceria usually consists of tetravalent and trivalent cerium). In this way, it is considered that the divalent cation, the trivalent cation and the tetravalent cation are the constituent components of the newly formed cluster, and these different valences coexist in the cluster (cluster). The total charge is, of course, compensated to be neutral by the amount of oxygen defects and the like). Since it is generally known that charge transfer is promoted on the surface of a material in which different valences coexist, electrons move in the complex cluster formation region, and the matrix is originally an oxide having an oxygen defect structure. By diffusing the oxide ion in the immediate vicinity, both the electron and the oxide ion can reach the place very close to the cluster. Furthermore, if the anode layer has good porosity, the gas (hydrogen) will also come into contact with many of the places where electrons and oxide ions can reach. Since this state occurs everywhere near the surface, it is thought that a new three-phase interface state will be created there, and as a result, the number of three-phase interfaces encountered by gas, electrons, and ions is naturally large even on the oxide surface. To increase.

Therefore, in the anode material of the present invention, a three-phase interface that functions as an active site can be provided everywhere on the surface of either Ni or oxide, and therefore, extremely high activity is realized as compared with the conventional anode material. It becomes possible to do.

Further, the oxide electrolyte is usually used in the form of a powder, but the fine particles constituting this powder may have a spherical shape or other low aspect ratio shape as in the case of a normal powder, or may be a nanowire. It may have a high aspect ratio. Therefore, it should be noted that the term "powder" in the present application does not exclude the case where some or all of the fine particles constituting the "powder" have a high aspect ratio such as nanowires.

In the present invention, when Rh, Pd, and Ru, which are platinum group elements, are used as constituents of the anode, and more generally, when a divalent cation is used, the ionic radius is within ± 10% of the ionic radius of Pt ²⁺ . Improve the power generation performance of solid oxide fuel cells by using. Here, as can be seen from the examples, among the three types of platinum group elements among the above elements, a particularly remarkable effect is exhibited when Rh is used. Not only for electrode catalysts, but also for catalysts in general, it is said that the catalytic action becomes stronger when the d-orbital is almost or just seen (see, for example, page 10 of Non-Patent Document 8). Therefore, a comparison of the electron configurations of Pt used in Patent Document 1 and Rh, Pd, and Ru used in the present invention is as follows.
Pt 4f14 5d9 6s1
Rh 4d8 5s1
Ru 4d7 5s1
Pd 4d10
Considering the electron configuration shown above, Pt and Pd should have higher electrode catalytic ability than the other two elements Rh and Ru. However, as can be seen from the following examples, when the experimental results at 700 ° C. are compared, it can be seen that when Rh is used, the activity is even higher than that of Pt and Pd. Therefore, the effect when Pt revealed in Patent Document 1 is used is exhibited by other platinum group elements Rh, Pd and Ru, and other above-mentioned elements, but in the case of Rh, the above-mentioned catalytic ability is exhibited. A great effect beyond what is expected from the general theory of height can be obtained.

As a result of further research on the possibility of using metal elements other than the platinum group by the inventor of the present application, not only the above-mentioned FeOx but also a small amount of MnOx vapor deposition and subsequent hydrogen reduction treatment have extremely high performance. Confirmed that improvement will be achieved. The experimental results are shown in Examples. Here, when MnOx was used, a large performance improvement was observed even if the vapor deposition thickness of MnOx was made extremely thin to 1 nm. Specifically, an anode having a vapor deposition thickness of 1 nm was used at an operating temperature of 700 ° C., and the current density at a cell voltage (IR-free) = 0.8 V was compared with that using other metal oxides in the examples. Then, the largest current density was obtained (Fig. 17). When RhOx was used, a current density slightly smaller than that of MnOx was obtained, and with FeOx, the next highest current density was obtained.

Even if the vapor deposition thickness was 10 nm, almost the same current density as in the case of 1 nm was obtained (FIG. 18), and it was found that a vapor deposition thickness of 10 nm or less was sufficient for the formation of desirable active sites. Even when the current density of cell voltage (IR free) = 0.8V is compared when the vapor deposition thickness is 10 nm and other metal oxides are used, it is much higher than that of RhOx vapor deposition (FIG. 11). It was confirmed that the output current (about 97% in the case of RhOx) with a slightly small current density can be obtained, which is a high performance. However, if the performance improvement is hindered by other factors when the vapor deposition thickness is increased, there is a possibility that the performance can be further improved by removing the factors. Therefore, it should be noted that the present invention does not preclude the deposition thickness of MnOx from being thicker than 10 nm.

Specifically, tetravalent Mn may hardly contribute to the improvement of performance by adding Mn. If so, no improvement in performance was seen when the MnOx vapor deposition thickness was increased to 10 nm, and the characteristics were almost the same as those at 1 nm because the tetravalent value was obtained when the MnOx vapor deposition thickness was increased. Since the ratio of Mn has also increased, it may be considered that the amount of trivalent Mn that contributes to the improvement of performance has hardly changed.

Here, the reason why the interface structure formed by Mn, Rh, and Fe is useful for improving the anode characteristics of the fuel cell will be described below with reference to FIGS. 4 to 7.

Since any of these metal elements can exist in a stable state as trivalent or tetravalent ions, in the following, these ions are Rh ³⁺ , Fe ³⁺ , and Mn ⁴⁺ ions (hereinafter, these ions are referred to in the figure) on the surface of the anode material. The explanation will be given assuming that a cluster is formed in a state where it is collectively referred to as M). As described above, a divalent ion, here Mn ²⁺ , or the like is used as a representative, and the ionic radius is adopted, or when the ionic radius is not reported, it is estimated. In addition, YSZ is used as the oxide electrolyte. In FIG. 4, a cluster having any structure centered on these ions is formed on the surface of NiO (as described with reference to FIG. 1, when a thin film such as RhOx is formed, the anode layer is an oxide in a fine particle state. It is a mixture of an electrolyte and NiO, and it should be noted that NiOx is reduced to metallic Ni by hydrogen reduction after thin film formation).

YSZ having a fluorite-shaped crystal structure (cubic crystal) in the anode layer shown in FIG. 4 (a) and NiO having a NaCl-shaped crystal structure (cubic crystal) also shown in FIG. 4 (b). Although the interface is an interface between the same cubic crystals, a large mismatch occurs. Due to the large mismatch (naturally, many lattice defects are generated in the vicinity) occurring at the interface between YSZ and NiO, a very small amount of Rh cation, Fe cation, and Mn cation are added to NiO during hydrogen reduction. Clusters are formed with residual oxygen and lattice defects on the surface. Such a cluster is shown in FIG. 4 (c). As the radius of the cation increases, the area occupied by the cluster will gradually expand, so the role as a buffer zone will be even more effective. In FIG. 4, Rh is assumed to be Rh ²⁺ as such a cation M, and Fe and Mn are also considered in the cluster as ionic species representing Fe ²⁺ and Mn ²⁺ , respectively. Please be careful. That is, in the following description and the drawings referred to therein, Rh, Fe, and Mn are all expressed as divalent ions. At this time, since the surface of Ni also has a NaCl-type crystal structure, a plane four-coordination structure of oxygen atoms (see the upper part of FIG. 4B) exists around Ni, which is formed as described above. The resulting clusters form a pyramidal five-coordination structure (see top of FIG. 4 (c)) apparently visible on the YSZ surface. Since the clusters thus formed on the NiO surface remain on the Ni surface even after hydrogen reduction, when the crystal structures on the surfaces of YSZ and Ni are compared, the cluster portion has a structure similar to that of YSZ. ..

Further, it is considered that the clusters formed as described above associate with each other in the formation process, and at that time, the distance between the clusters is close to the size of the unit cell assumed on the YSZ surface. It can be said that this indicates from the viewpoint of modeling that the ionic radii of Rh ²⁺ (also Fe ²⁺ and Mn ²⁺ ) are large enough to easily form a cluster of the assumed size.

The left side of FIG. 5A is YSZ, and the right side is a NiO surface unit cell (as shown in FIG. 6, the smallest hexagon that can represent a cluster is a region consisting of 4 vertical and 6 horizontal). The size of the unit cell is shown. In FIG. 6, as described immediately above, six smallest hexagons are lined up in the horizontal direction, but in the vertical direction, there are arrays that cannot form the smallest unit hexagon, so the intervals are evenly spaced. It is open and the number is four. Therefore, the vertical and horizontal lengths do not correspond to the number of hexagons. On the other hand, the right side of FIG. 5B shows the distance between the associated surface defect clusters and the surface defect clusters there. Comparing (a) and (b) in FIG. 5, the size of the unit cell of YSZ is 17.9 Å and 23.9 Å, whereas the corresponding size is 17 on the associated surface defect cluster side, respectively. It can be seen that they are very close to 0.0 to 17.9 Å and 23.0 to 23.9 Å. Here, when Rh ²⁺ , Fe ²⁺ , and Mn ²⁺ are used, as mentioned earlier, when the radius of the cations constituting the cluster (assumed to be represented by +2) becomes large, the area occupied by the cluster becomes a little. Since it is thought that it will spread gradually, the effect will be remarkable if the cluster size has a range and the role as a buffer zone is further increased.

A part of the NiO surface shown on the right side of FIG. 3B is drawn in a slightly darker color than the other parts, which indicates that surface defect clusters are formed in this part.

Based on the above, the reason why such a surface defect cluster promotes the anodic reaction will be described with reference to FIG. 7.

FIG. 7A illustrates the progress of the anode reaction on the conventional anode, and FIG. 7B schematically shows the progress of the anode reaction on the anode in which surface defect clusters are formed on the Ni surface as described above. Shown. As for the conventional anode reaction, a model of the reaction has been proposed by first-principles calculation. The details will be complicated and will not be described here, but if necessary, refer to Non-Patent Document 10 and other documents referred to therein.

The left side of FIG. 7 shows a relatively wide region near the interface between YSZ and Ni in the anode, and the right side shows an enlarged narrow region surrounded by a horizontally long broken line in the region shown on the left side.

As described above, when a surface defect structure similar to the YSZ surface is formed on the Ni surface and the size of the unit cell is apparently very close to each other, a water molecule formation reaction (fuel cell) that has conventionally occurred only on the YSZ surface. It is considered that surface oxygen diffusion, which was considered to be the slowest reaction in the anode reaction), also occurs on the Ni surface. As a result, as shown in FIG. 7 (b), it is possible to easily cause a water molecule formation reaction on both the YSZ surface and the Ni surface, and as a result, it is possible to bring out excellent performance. Be done.

In generalizing the performance improving action as described above, in order to achieve the performance improving action described with reference to FIGS. 4 to 7, as described with reference to FIG. 5 and the like, the oxide electrolyte It is required that the unit lattice size of the above is close to the distance at which the associated surface defect clusters are associated. Naturally, the size of the surface defect cluster is affected by the radius of the tracely added metal ions constituting the cluster. In the study by the present inventor, it is considered that such a metal ion is an ionic species representing a divalent ion, and the ionic radius of the divalent ion falls within the range of ± 10% of the ionic radius of Pt ²⁺ . It was found that the performance improvement effect was effectively exhibited. The ionic radii of the divalent cations of Rh and Fe are within the range of ± 10% as already examined. It is also known that the ionic radius of the divalent cation of Mn is 0.82 Å, which is also within ± 10% of the ionic radius of Pt ²⁺ .

The above explanation was for the case where zirconia (ZrO ₂ ) was used as the oxide electrolyte, but this explanation holds even when zirconia is replaced with ceria (CeO ₂ ). As can be seen from FIGS. 8 and 9, even when zirconia is replaced with ceria, a large lattice misfit occurs with NiO. Here, when Mn is used as the metal to be added in a small amount, assuming that Mn ²⁺ is a representative, a cation having an ionic radius of 0.82 Å (this is within ± 10% with respect to the ionic radius of 0.80 Å of Pt ²⁺ ). Form a cluster. Therefore, as in the case where zirconia is used as the oxide electrolyte, the inter-cluster distance in the associative surface defect clusters is close to the inter-lattice distance of ceria. This alleviates the large grid misfit between NiO and CeO ₂ .

As described above, the present invention provides an anode material for realizing a solid oxide fuel cell that operates even at a low temperature of about 650 to 700 ° C. by adding an extremely small amount of metal element. Here, the specific range of the amount of metal to be added is considered to be about 4 to 400 ppm of the anode material. However, from the viewpoint of the operating principle of the present invention and the experimental results, it is expected that this range is further expanded for both the upper limit and the lower limit.

[Manufacturing, measurement, and evaluation of the anode material of the present invention and a solid oxide fuel cell using the same]
In the examples described below, comparative examples and examples in which the conventional cathode material and the anode material of the embodiment of the present invention are formed on the two surfaces of the solid electrolyte pellet for a solid oxide fuel cell are prepared. The characteristics of the solid oxide fuel cell single cell using the above were evaluated.

Specifically, the single cell of the comparative example was prepared as follows. First, an anode (NiO-8YSZ) slurry was applied to one side of a pellet (thickness: 500 μm, diameter 10 mm) of a zirconia (8YSZ) sintered body in which 8 mol% yttrium was dissolved by a screen printing method and dried. .. The composition of the solid content in this anode (NiO-8YSZ) slurry was NiO: 8YSZ = 4: 1 (weight ratio). Then, it was baked in air at 1200 ° C. for 1 hour and slowly cooled to room temperature. Next, a cathode ((La _0.80 Sr _0.20 ) _0.95 MnO _3-x : manufactured by Fuel cell materials, product name LSM20-I) slurry was applied to the other surface, dried, and then 1100. The baking treatment was performed in air at a temperature of ° C. for 1 hour. After the baking treatment, NiO in the anode layer was reduced using 4% hydrogen (helium diluted) gas at a temperature of 800 ° C. Since large voids are generated in the anode layer when NiO is reduced to Ni, a solid oxide fuel cell single cell in which the anode layer is a porous body is obtained.

On the other hand, in producing the examples of the present invention, first, as in the comparative example, a NiO-8YSZ (NiO: 8YSZ = 4: 1 (weight ratio)) anode is baked onto pellets of the same type and thickness, and further. A cathode ((La _0.80 Sr _0.20 ) _0.95 MnO _3-x : manufactured by Fuel cell materials, product name LSM20-I) slurry was applied to one surface, dried, and then at a temperature of 1100 ° C. The baking treatment was performed in the air for 1 hour. Then, a rhodium oxide (RhOx) film was formed on the NiO-8YSZ anode. The RhOx film was formed on the anode by a magnetron sputtering method using a rhodium target (purity: 99.95%) having a diameter of about 5 cm. Here, a sample was placed at a location 90 mm away from the rhodium target, and DC sputtering was performed using a DC power supply of 10 W at room temperature under an oxygen partial pressure of 4 × 10 ^-1 Pa. The formation of RuOx on the anode was performed at a rate of about 2 nm per minute. After forming RhOx films having three thicknesses of 1 nm, 5 nm and 10 nm on the anode layer, NiO was reduced at a temperature of 800 ° C. using 4% hydrogen (helium diluted) gas for comparison. As in the example, the anode layer was a porous body. The content of Rh in the anode layer thus prepared was measured. As a result, it was 65 mg / kg (65 ppm) when the film thickness of RhOx was 10 nm, and 6.5 mg / kg (6.5 ppm) when the film thickness was 1 nm. The amount of Rh in the anode layer was measured by inductively coupled plasma mass spectrometry (ICP-MS) (device used: PerkinElmer ELAN DRCII ICP-MS).

In this embodiment, a DC sputtering apparatus was used for sputtering, but any film forming means such as an AC sputtering apparatus can be used as long as the required RhOx film can be formed.

Further, by exchanging the target with a ruthenium target and a palladium target, ruthenium oxide (RuOx) films having a thickness of 1 nm, 5 nm and 10 nm and palladium (PdOx) films having a thickness of 1 nm and 10 nm were formed by the same method, respectively. An anode was made.

As can be seen from the above explanation, all the films of RhOx, RuOx and PdOx (hereinafter, may be represented by RhOx and referred to as RhOx or the like) on the anode side were performed after the baking on the cathode side. The reason is that after forming a film such as RhOx, further heat treatment at 1100 ° C. for 1 hour results in grain growth of RhOx or the like itself, which is described below for reduction of RhOx or the like. This is because it may adversely affect the diffusion of Rh, Ru and Pd cations during the treatment process and the formation of Rh, Ru and Pd cation-defect oxide-Ni cation clusters.

Here, the particle sizes of NiO and 8YSZ used have a preferable range. If NiOx is unnecessarily fine, it will sinter itself and the connection between NiOx will be broken. Therefore, when producing this kind of anode, particles on the order of microns are usually used. If the 8YSZ is too large, NiOx may not sufficiently contact the connecting portion between the 8YSZs, so powder having a particle size of submicron to micron order is usually used here as well. In this example and comparative example, 8YSZ used TZ-8YS grade powder manufactured by Tosoh Corporation, and NiO used NIO-F grade powder manufactured by Fuel cell materials.

According to Tosoh Corporation, the BET specific surface area of TZ-8YS grade powder, which is 8YSZ, is about 7 m ² g ^-1 . Normally, in the case of a BET specific surface area of this degree, the average particle size is 2 to 3 μm, so it is considered that the average particle size of the 8YSZ used here is also about 2 to 3 μm (note that the average particle size is also about 2 to 3 μm). If is in the submicron, the BET specific surface area will be double digits).

The BET specific surface area of the NIO-F grade powder used as the NiOx powder was about 3.1 m ² g ^-1 , which is almost half of that (described on the purchased bottle). The average particle size is estimated to be about twice as large as 8YSZ.

When powders other than those used in the examples are used, the BET specific surface areas of 8YSZ and NiO are within the range of about 7 m ² g ^-1 ± 20%, respectively, and about 3.1 m ² g ^-1 ± 20%. Is considered to be suitable. If the BET specific surface area is too small (that is, the average particle size is too large), the surface area where the active site can exist decreases, so that the activity as an electrode catalyst naturally decreases. On the contrary, when the BET specific surface area is excessive (that is, the average particle size is too small), the high temperature treatment exceeding 1000 ° C. is performed during the baking process, so that the grain growth progresses and the connection between NiOx and 8YSZ is lost. On the contrary, the charge transfer path and the oxide ion diffusion path in the anode layer are cut off, which reduces the ratio of the three-phase interface in the anode layer, which is not preferable.

The examples thus produced (that is, the film thicknesses of RhOx, PdOx, and RuOx formed to contain Rh, Pd, and Ru in the anode layer are 1 nm, 5 nm, and 10 nm in the case of PhOx and RuOx. Three ways, PdOx is 1 nm and 10 nm) and the solid oxide fuel cell single cell of the comparative example were operated as a solid oxide fuel cell, and the relationship between the current density and the cell voltage was measured. Pure hydrogen (room temperature, water saturation) was supplied as an anode gas at a flow rate of 80 sccm, and pure oxygen was supplied as a cathode gas at a flow rate of 80 sccm (actually, the above reduction treatment was first performed at 800 ° C. in a power generation device. After that, the gas to be supplied was switched to generate electricity and measure). The operating temperature of the solid oxide fuel cell single cell in this power generation test was usually 1000 ° C, but in this experiment, it was set to 650 ° C and 700 ° C. In obtaining the measurement data, a holding time of about 10 minutes was taken for the measurement of one point, and the measured value was used as the measured value of the measurement point after waiting for the measured value to stabilize. Thereby, the current density-IR free (net cell voltage compensated for the influence of the voltage drop due to the internal resistance of the fuel cell) characteristic (operating temperature 800 ° C.) was obtained for the single cell of the above embodiment.

It should be noted that the method of obtaining IR-free is a matter well known to those skilled in the art, and FIG. 2 shows an outline of the method of obtaining it by the current cutoff method. As the name suggests, the output current from the fuel cell is changed as steeply as possible from the state in which the predetermined current i is flowing to the current 0, as shown in the upper graph of FIG. This can be achieved by inserting an oscilloscope into the circuit that extracts current from the fuel cell, setting this steep current change, and observing the voltage change waveform due to this. IR-free measurement is the net voltage drop IR of the fuel cell, which compensates for the ohmic voltage drop IR due to the internal resistance R of the fuel cell system with respect to the cell voltage V of the fuel cell when a given current I is output. The cell voltage Vo is obtained. When the output current of the fuel cell is suddenly cut off, the cell voltage rises immediately by the ohmic voltage drop in the simple model of the series circuit of the current source with internal resistance 0 and the internal resistance R, but in the actual fuel cell, there are various types. Since the lagging element of is included in the system, the cell voltage is not vertical at the rising edge immediately after cutting as shown in the lower graph of FIG. 12, and changes slightly even after the transition from the rising edge region to the steady region (). In the graph at the bottom of FIG. 12, it gradually rises and converges to a constant value). Therefore, in the graph on the lower side of FIG. 2, the cell voltage coordinates at the intersection of the vertical extension line from the time when the cell voltage starts to change due to the current cutoff and the extension line of the cell voltage change immediately after the transition to the steady state. Let the reading be ohmic (IR) voltage drop Vo. As a result, IR-free becomes IR-free = V + Vo
It is sought as.

The current density-IR-free graphs obtained as described above are shown in FIGS. 10 to 15. The combination of the operating temperature of the solid oxide fuel cell single cell and the platinum group metal element added to the anode layer is 650 ° C.-Rh, 700 ° C.-Rh, 650 ° C.-Pd, 700, respectively, for FIGS. 10 to 15. ° C.-Pd, 650 ° C.-Ru and 700 ° C.-Ru.

Further, in order to verify that the element that can be contained in the anode is not limited to the platinum group element and the ionic radius is important when the divalent cation is used, the anode containing Fe is used as the above-mentioned platinum group element. It was produced by the same method as in the case of. That is, first, the NiO-8YSZ (NiO: 8YSZ = 4: 1 (weight ratio)) anode is baked onto pellets of the same type and thickness as in the case of Rh or the like described above, and further, in the case of Rh or the like on the other surface. The same cathode slurry was applied and dried, and then baked in air at a temperature of 1100 ° C. for 1 hour. Next, using an iron target as a target, iron oxide (FeOx) films having a film thickness of 1 nm and 10 nm were formed by the same method as in the case of Rh and the like. This was reduced to NiO using 4% hydrogen (helium diluted) gas at a temperature of 800 ° C. to prepare an Fe-containing anode having a porous anode layer like Rh and the like. Using the Fe-containing anode thus prepared, the same measurement as the anode containing Rh and the like was performed at 700 ° C. The result is shown in FIG. The data of "No FeOx" in FIG. 16 was obtained by using the comparative example described at the beginning of the embodiment as in the case of Rh and the like. There is no data on the Fe-containing anode at 650 ° C, but at 700 ° C, although it is not as good as Rh, the results are almost comparable to Pd and Ru.

As can be seen from these figures, in the conventional solid oxide fuel cell which does not contain Rh etc. in the anode layer, the current density is 25 mAcm ^- at the operating temperature of 650 ° C and 700 ° C when the IR free is 0.8 V. The value is extremely low, which is less than ² , and it does not substantially function as a fuel cell. On the other hand, when Rh is included in the anode layer (FIGS. 10 and 11), the current density when the IR free is 0.8 V is about 67 mAcm ^-2 at an operating temperature of 650 ° C, which is nearly three times that of the conventional one. In addition, although it changes depending on the content of Rh at 700 ° C., it showed a large value of 150 to 230 mAcm ^-2 , which was about 5 to 10 times larger than the conventional value. Further, as can be seen from FIGS. 12 to 16, the same tendency as that of Rh was shown when the anode layer contained Pd, Ru and Fe. Furthermore, in any of Rh, Pd, Ru, and Fe, even if the sputter thickness of the oxide layer for containing these elements in the anode layer is reduced to 1 nm, the current density is 10 nm as compared with the case of the film thickness. It has not dropped extremely. From this, it is considered that the content of these elements can be further reduced as compared with those tested in the examples without significantly deteriorating the performance as a fuel cell.

The table below shows the thickness and composition of the metal oxide film having the same composition and thickness as that used in the above examples, and the thickness and composition of the metal oxide film not used in the examples but can be used in the present invention. In addition, the atomic number density of the metal and the composition ratio of the metal in the anode material of the present invention prepared by the method described above by using this are expressed in ppm (that is, mass ratio mg / kg, the same applies hereinafter). (Sample numbers 3 to 21). This table also shows the anode materials (Sample Nos. 1 and 2) prepared using the PtOx membrane based on the invention of Patent Document 1.

This table shows the atomic number densities of the metals Pt, Rh, Ru, Pd, Fe in the anode material evaluated from the Rutherford Backscattering Spectroscopy (RBS) results of various metal oxide film samples. In addition, for some samples, the composition ratio of the metal in the anode material evaluated from the SEM-energy dispersive X-ray analysis (EDX) result is also shown. Further, in the column of chemical analysis results, the data obtained as a result of inductively coupled plasma mass spectrometry (ICP-MS) for sample numbers 1 and 2 are shown. Since ICP-MS has not been performed for sample numbers 3 and later, the composition ratios of the metals Ph, Ru, Pd, and Fe contained therein are proportional to the atomic number density obtained by RBS for samples 3 to 21. As a result of sample number 2, that is, the result of conversion based on the fact that the composition ratio of the metal was 91 ppm when the value of the atomic number density was 5.9 × 1015 ⁽ the first fraction after the decimal point in ppm display). (Rounded to the nearest whole number) is shown in this column. Looking at the metal composition ratios of Samples 3 to 21, the minimum is 4 ppm (Sample 14) and the maximum is 372 ppm (Sample 4). From this, if the composition ratio of the metal element in the anode material in which the ionic radius of the divalent cation is within the range of ± 10% of the ionic radius of Pt ²⁺ is in the range of about 4 to 400 ppm, the anode of the present invention is used. It turns out that the material is obtained. Considering the principle of the present invention and the experimental results described above, it is considered that the anode material of the present invention can maintain its high performance even if the composition ratio is further increased. As for the lower limit, even if the thickness of the metal oxide film is reduced to 1 nm, the performance does not decrease sharply. Therefore, in reality, an anode material having high performance can be obtained even with a composition ratio smaller than 4 ppm. it is conceivable that.

[Manufacturing, measurement, and evaluation of an anode material when MnOx is used as a thin film in the above example and a solid oxide fuel cell using the anode material]
By using the same materials, equipment, and methods as in the above embodiment except that the target for DC sputtering was replaced with a manganese target to form MnOx thin films having a thickness of 1 nm and 10 nm, a single cell using Mn was used. It was created. This single cell was operated as a solid oxide fuel cell, and the relationship between the current density and the cell voltage was measured. It is considered that the concentrations of Mn in the anode prepared with the thickness of the thin-film deposition film of MnOx being 1 nm and 10 nm are 54 ppm and 390 ppm, respectively.

Figure shows the measurement results of cell voltage (IR-free) characteristics when a single cell using an anode that was hydrogen-reduced at 800 ° C after forming a 1 nm-thick MnOx film was operated as a solid oxide fuel cell at 700 ° C. 17 is shown. As can be seen, the current density at the cell voltage (IR-free) = 0.8 V is approximately 225 mA cm ^-2 , and the maximum current density in the example using the metal oxide thin film having a thickness of 1 nm can be achieved. rice field.

FIG. 18 shows the measurement results of the cell voltage (IR-free) under the same conditions except that the thickness of the MnOx film is 10 nm. As can be seen by comparing with the measurement results shown in FIG. 17, when the thickness of the MnOx film is 1 nm and 10 nm, such as when the current density at cell voltage (IR free) = 0.8 V is almost the same as when the thickness is 1 nm. The performance was almost the same. Therefore, it was found that a concentration of Mn in the anode of 400 ppm or less was sufficient for the formation of desirable active sites using MnOx. Comparing the measurement results of the cell voltage (IR-free) at an operating temperature of 700 ° C. when the film thickness is 10 nm, the current density at the cell voltage (IR-free) -0.8 V is higher than that of the RhOx film shown in FIG. Although it is very small, the result can be said to be almost the best among the examples.

As described in detail above, according to the present invention, even if a small amount of Rh or the like is contained in the anode layer, very high power generation performance can be exhibited, and the operating temperature range can be extended in the low temperature direction. A physical fuel cell can be provided.

In addition, in the research and development of electrodes for solid oxide fuel cells, the focus has been mainly on improving the cathode side, but it is expected that the anode side will also become important in the future. That is, when using a solid oxide fuel cell in a medium temperature range, it is generally considered that a solid electrolyte thin film (about 50 μm) is placed on a substrate made of an anode composition. This is because by doing so, the large resistance of the solid electrolyte can be reduced. A device can be made by applying a thin coat of cathode on it. However, this device has a thick anode layer. Specifically, if it is not about 1 mm, the device will be broken. Under such circumstances, it is said that the loss of the anode, which has been considered to be less of a concern in the conventional solid electrolyte-supported type, has a serious adverse effect on the efficiency of the entire fuel cell. Therefore, it is considered that efforts on the anode side will become the mainstream in the future. That is, in a thin film solid electrolyte device, since the anode is used as a substrate, it is important to reduce the resistance thereof.

Therefore, the present invention is expected to greatly contribute to the practical application and popularization of solid oxide fuel cells.

JP-A-2017-004957

William C. Chueh, Yong Hao, WooChul Jung and Sossiana M. Haile, Nature Mater., 11, 155-161, (2012). http://www.nature.com/nmat/journal/v11/n2/extref/nmat3184-s1.pdf M.Watanabe, H.Uchida, M.Shibata, N.Mochizuki, K.Amikura,'High Performance Catalyzed-reaction Layer for Medium Temperature Operating Solid Oxide Fuel Cells.' J. Elechtrochem. Soc. 1994, 141, 342-346 .. Keisuke Fugane, Toshiyuki Mori, Pengfe Yan, Takaya Masuda, Sunya Ymamoto, Fei Ye, Hideki Yoshikawa, Graeme Auchterlonie, and John Drennan, ASC Appl. Materi. Interfaces 7, 2698-2707 (2015). Zhi-Peng Li, Toshiyuki Mori, Graeme John Auchterlonie, Jin Zou and John Drennan, Phys. Chem. Chem. Phys. Vol.13 (20), 9685-9690 (2011). Zhi-Peng Li, Toshiyuki Mori, Graeme John Auchterlonie, Yanan Guo, Jin Zou, John Drennan, and Masaru Miyayama, J. Phys. Chem. C, Vol.115 (14), 6877-6885 (2011). Ding Rong Ou, Toshiyuki Mori, Hirotaka Togasaki, Motoi Takahashi, Fei Ye, and John Drennan, Langmuir, 27, 3859-3866 (2011). Katsuaki Sato "Electronic Structure of Metals-For Understanding Catalysts-" 6th New Electrodecatalyst Symposium & Accommodation Seminar (November 11-12, 2013, Venue: Karuizawa, Materials Science and Technology Promotion Foundation) Training Center, Organizer: (One company) Fuel Cell Related Catalyst Study Group, Fuel Cell Development Information Center (FCDIC), FC Roundtable (http://home.sato-gallery.com/research/electronic_structure_of_metals.pdf) R D Shannon, Acta Crsytallogr., Sect. A: Found Crsyatallogr. 1976, 32, pp.751-767. Shixue Liu, Arief Muhammad, Kazuya Mihara, Takayoshi Ishimoto, Tomofumi Tada, and Michihisa Koyama, J. Phys. Chem. C, 121, 19069-19079 (2017).

Claims (16)

An anode material containing zirconia or ceria, nickel and one or more metal elements (except platinum alone).
The metal element has a divalent cation ionic radius within ± 10% of the platinum divalent cation ionic radius .
The composition ratio of the metal element to the anode material is in the range of 4 to 400 ppm.
Anode material for solid oxide fuel cells. One or more metal elements whose ionic radius is within ± 10% of the ionic radius of the divalent cation of platinum when zirconia or ceria, nickel and divalent cations are used (however, the metal element is platinum alone). Includes (except when) and
The metal element does not exist at the interface between zirconia or ceria and nickel as particles having a diameter of 1 nm or more.
Anode material for solid oxide fuel cells. One or more metal elements whose ionic radius is within ± 10% of the ionic radius of the divalent cation of platinum when zirconia or ceria, nickel and divalent cations are used (however, the metal element is platinum alone). Includes (except when) and
The metal element takes the form of a defect association cluster in which the cation and nickel defects of the metal element and the oxygen defects created to balance these cation defects and charges are combined.
Anode material for solid oxide fuel cells. The anode material for a solid oxide fuel cell according to any one of claims 1 to 3, which functions as an anode of the solid oxide fuel cell at 700 ° C. The metal element is one or more selected from the group consisting of rhodium, ruthenium, palladium, iron and zinc, or one or more of the selected elements plus platinum. 4. The anode material of the solid oxide fuel cell according to any one of 4. The anode material for a solid oxide fuel cell according to any one of claims 1 to 4, wherein the metal element is manganese, or manganese is further added with platinum. The anode material for a solid oxide fuel cell according to claim 6, wherein the metal element further comprises one or more selected from the group consisting of rhodium, ruthenium, palladium, iron and zinc. The anode material for a solid oxide fuel cell according to any one of claims 1 to 7, which has a porous structure. The anode material for a solid oxide fuel cell according to any one of claims 1 to 8, wherein the zirconia is yttria-stabilized zirconia. An oxide film of the metal element is formed on a layer of a mixture of zirconia or ceria powder and nickel oxide powder.
The layer of the mixture on which the oxide film was formed was heated in a hydrogen atmosphere of pure hydrogen or diluted hydrogen, and the mixture was heated.
Diffuses the metal element cations from the oxide film into the layer and reduces nickel oxide in the layer.
The method for producing an anode material for a solid oxide fuel cell according to any one of claims 1 to 9. The method for producing an anode material for a solid oxide fuel cell according to claim 10, wherein at least a part of the particles constituting the zirconia or ceria powder are nanowires. The method for producing an anode material for a solid oxide fuel cell according to claim 10 or 11, wherein a porous structure is formed in the layer by heating the mixture in the hydrogen atmosphere. The method for producing an anode material for a solid oxide fuel cell according to any one of claims 10 to 12, wherein the layer of the mixture is formed from a slurry of zirconia or ceria powder and nickel oxide powder. The method for producing an anode material for a solid oxide fuel cell according to claim 13, wherein a baking process is performed after the formation of the layer of the mixture from the slurry . The method for producing an anode material for a solid oxide fuel cell according to any one of claims 10 to 14, wherein the oxide film is formed by sputtering. A solid oxide fuel cell having an anode using the anode material according to any one of claims 1 to 9.

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