JP2015099744A - Material for fuel batteries and utilization thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a material for fuel batteries capable of suppressing the problem of migration over a long period of time even when used in an electric field at a high temperature (e.g., about 600-800°C) while including Ag.SOLUTION: A material for fuel batteries comprises a perovskite-type crystal structure and is composed of an oxide in which Ag is solid-solved in the crystal structure. The oxide is preferably represented by the following general formula: (Ln,Ae)(MAg)O(where Ln represents one or two or more kinds of elements selected from lanthanoid series; Ae represents at least one element selected from a group consisting of Ca, Sr and Ba; M represents one or two or more kinds of elements selected from a group consisting of Co, Mn, Cr, Cu, Fe, Ni and Ti; x and y satisfy 0≤x<1 and 0<y<0.15 respectively; and δ is a value determined so as to meet a requirement for charge neutralization).

Description

  The present invention relates to a fuel cell material and use thereof. Specifically, the present invention relates to a fuel cell material that can be suitably used for the construction of an air electrode of a solid oxide fuel cell.

Solid oxide fuel cells (SOFC), also called solid electrolyte fuel cells (hereinafter sometimes referred to simply as “SOFC”), have high power generation efficiency among various types of fuel cells. The load of the fuel is low, and various fuels can be used. An SOFC single cell is essentially composed of a dense layered solid electrolyte made of oxygen ion conductor, and a porous structure air electrode (cathode) is formed on one side of the solid electrolyte, A fuel electrode (anode) having a porous structure is formed on the surface. Here, an O ₂ (oxygen) -containing gas typified by air or the like is supplied to the surface of the solid electrolyte on the side where the air electrode is formed, and the surface of the solid electrolyte on the side where the fuel electrode is formed, A combustible fuel gas represented by H ₂ (hydrogen) is supplied. In general operation, O ₂ gas in the air is reduced at the cathode to become O ²⁻ anion, passes through the solid electrolyte, and generates electrical energy as the H ₂ gas fuel is oxidized at the anode. I am letting.

  Such SOFC has been conventionally operated at a high temperature of 650 ° C. or higher (typically about 700 ° C. to 900 ° C.). However, in recent years, such an operation has been performed from the viewpoint of improving durability and reducing costs. It is desired to lower the temperature. For example, it has been studied to reduce the operating temperature of SOFC to about 600 ° C. However, when the SOFC is operated at a low temperature, there is a problem that the overvoltage at the air electrode is increased and the cell performance (for example, power density) is lowered. Therefore, in order to reduce such overvoltage, attempts have been made to add silver (Ag) as a catalyst to the air electrode. For example, Patent Documents 1 and 2 are known as conventional techniques related to an SOFC air electrode forming material containing Ag.

JP 2012-230794 A Japanese Patent No. 5182850

  However, even when the operating temperature of the SOFC is reduced to about 600 ° C., if an electric field is generated around the cell due to the operation of the SOFC, Ag contained in the air electrode undergoes migration due to the potential gradient, and the performance of the SOFC There was a problem of damage. For example, Ag contained in the air electrode may diffuse into a solid electrolyte, other SOFC insulating members, or the like, thereby losing the insulating properties of such parts. In addition, when the Ag component diffuses to the vicinity of the solid electrolyte / electrode interface in the operation of the SOFC, a current leak layer may be formed between the solid electrolyte and the air electrode, thereby reducing the cell performance.

  The present invention has been created to solve the above-mentioned conventional problems. The object of the present invention is to use Ag in a low to high temperature (for example, about 600 ° C. to 800 ° C.) electric field while containing Ag. It is an object of the present invention to provide a fuel cell material capable of suppressing the problem caused by the migration over a long period of time. Another object of the present invention is to provide an air electrode using such a fuel cell material, and an SOFC provided with such an air electrode.

In order to solve the above problems, the invention disclosed herein provides a fuel cell material. Such a fuel cell material has a perovskite type crystal structure, and is characterized by comprising an oxide in which Ag is dissolved in the crystal structure.
Ag is a component that exhibits excellent electrical conductivity and has a catalytic action. For example, Ag is contained in an oxide material having a perovskite crystal structure, thereby improving the electrical characteristics of the oxide. , Can provide catalytic action. That is, the cell characteristics of the fuel cell can be improved by forming the electrode, current collector, and the like of the fuel cell with the oxide material containing Ag. Further, since Ag is taken into the crystal structure of the oxide, for example, even when it is placed in an electric field, Ag is prevented from moving and diffusing according to the potential gradient. Therefore, according to such a configuration, a fuel cell material provided with Ag migration resistance in addition to the electrical characteristics and catalytic activity inherent in the Ag component are provided.

In a preferred embodiment of the fuel cell material disclosed herein, the oxide has the following general formula:
_{(Ln 1-x Ae x)} (M 1-y Ag y) O 3-δ
It is characterized by being indicated by. Here, in the formula, Ln is one or more elements selected from lanthanoids. Ae is one or more elements selected from the group consisting of Ca, Sr and Ba. M is one or more elements selected from the group consisting of Co, Mn, Cr, Cu, Fe, Ni, and Ti. X and y satisfy 0 ≦ x <1 and 0 <y <0.15, respectively. Δ is a value determined so as to satisfy the charge neutrality condition.
The perovskite oxide represented by the above general formula can be an ion-electron mixed conduction material having both good ionic conductivity and electron conductivity. According to such a configuration, the action of Ag is imparted to such an ion-electron mixed conductive material, and migration thereof can be suppressed.

In a preferred aspect of the fuel cell material disclosed herein, the M is characterized by being Co or Fe or both.
According to such a configuration, for example, the perovskite oxide represented by the above general formula can be provided with characteristics that are particularly favorable as an SOFC air electrode material. Therefore, for example, a fuel cell material capable of producing an SOFC excellent in cell performance (for example, power density) is provided.

In a preferred embodiment of the fuel cell material disclosed herein, the above y is characterized by satisfying 0.0001 ≦ y ≦ 0.1.
With such a configuration, Ag can be more stably dissolved in the perovskite crystal structure. For example, a member made of such a material for a fuel cell is preferable because the movement and diffusion of Ag can be suitably suppressed even in a temperature region of 600 ° C. or higher or in an electric field.

In another aspect, the invention disclosed herein provides a fuel cell component. Such a fuel cell component is composed of any one of the fuel cell materials described above.
According to such a configuration, for example, a fuel cell constituent member having migration resistance in which occurrence of Ag migration is suppressed even when used in an electric field is provided.
For example, the fuel electric component is preferably a SOFC air electrode or a current collector. In particular, by configuring the SOFC air electrode with such fuel cell components, overvoltage of the air electrode can be suppressed even when operated at a temperature of about 600 ° C., and cell performance (for example, output density) ) Can be improved. Further, since migration of Ag is suppressed, such high cell performance can be realized over a long period of time. That is, the invention disclosed herein can provide an SOFC capable of maintaining excellent cell performance over a long period of time.

It is a cross-sectional schematic diagram explaining one form of the SOFC system provided with the cylindrical anode support type SOFC (single cell). It is an exploded perspective view showing typically one form of SOFC system provided with stack-like SOFC (single cell). It is the figure which illustrated the X-ray-diffraction pattern of the material for fuel cells disclosed here.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, a general configuration of SOFC that does not characterize the present invention, a manufacturing process, an operating method, etc.) Can be understood as a design matter of those skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  The fuel cell material disclosed herein is characterized by being essentially composed of an oxide having a perovskite-type crystal structure in which Ag is dissolved in the crystal structure. That is, Ag is solid-dissolved in the oxide having the perovskite crystal structure (hereinafter, the oxide having the perovskite crystal structure is also simply referred to as “perovskite oxide”). The characteristics derived from Ag can be suitably imparted to the fuel cell material. Hereinafter, the fuel cell material having such a configuration will be described in detail.

[Perovskite oxide]
The fuel cell material disclosed herein typically includes an oxide having a perovskite crystal structure represented by ABO ₃ . Here, A and B are metal elements, and typically, A can be a monovalent alkali metal, a divalent alkaline earth metal, a trivalent light rare earth element, or the like. B may be a transition metal, a typical metal, a rare earth element, or the like that can be a trivalent or higher ion. And in one more preferable form as a fuel cell material, such a perovskite type oxide may have a composition represented by the following general formula. That is, the perovskite oxide is more preferably a perovskite complex oxide represented by the following general formula.
_{(Ln 1-x Ae x)} (M 1-y Ag y) O 3-δ

Such a perovskite oxide can be understood as a structure in which a part of the Ln (lanthanoid) element at the A site is replaced with Ae and a part of the M element at the B site is replaced with Ag.
Here, in the formula, Ln is a lanthanoid element having an atomic number of 57 to 71. As such Ln, 15 elements from lanthanum (Ln) to lutetium (Lu) can be considered. Ln may be contained alone from any one of these 15 types of lanthanoid elements, or may be contained in combination of two or more. As such a lanthanoid, specifically, an element having a relatively large ionic radius such as lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm) is preferable. . Among these, it is preferable that the lanthanoid is La because a more stable crystal structure can be formed. When the lanthanoid contains elements other than La together with La, the ratio of La is preferably high.

  Ae is an element that can be substituted for the lanthanoid (Ln) as described above, and can be calcium (Ca), strontium (Sr), or barium (Ba). Any one of these elements may be contained alone, or two or more of these elements may be contained in combination. Especially, the form containing Sr is preferable. When two or more elements are included as Ae, it is further preferable that Sr is included at a higher content.

  M is an element that can constitute the B site of the perovskite oxide as described above, and can preferably be a transition metal element. Specifically, it can be cobalt (Co), manganese (Mn), chromium (Cr), copper (Cu), nickel (Ni), iron (Fe) and titanium (Ti). Any one of these elements may be contained alone, or two or more of these elements may be contained in combination. Since the perovskite oxide contains these elements (so-called transition metal elements) at the B site, the d electrons of the transition metal ions are localized, and can exhibit high electrical conductivity. Further, when the transition metal occupies the B site, the valence of the transition metal ions may change depending on the surrounding environment. For example, in a high-temperature reducing atmosphere, the amount of oxygen is reduced from 3 and vacancies (oxygen defects). ) May be formed. Also, oxygen defects can be introduced by intentionally reducing the sum of the valences of metal ions at the A site and B site from +6. The perovskite oxide in which oxygen defects are introduced in this way can also be an oxygen ion conductor in which oxygen ions move quickly through oxygen defects. That is, the fuel cell material disclosed herein can be, for example, a perovskite-type oxide ion electron mixed conductive material useful as an SOFC electrode material.

  Ag is silver (Ag), and may be a characteristic component contained in the perovskite oxide that constitutes the fuel cell material disclosed herein. In addition to having essentially excellent electrical conductivity, Ag can also exhibit catalytic activity. Therefore, by including such an Ag component, characteristics such as electrical conductivity and catalytic activity can be imparted to the perovskite oxide. In addition, this Ag is stably taken into the crystal structure of the perovskite oxide and fixed, for example, so that even if this fuel cell material is placed in an electric field, Ag diffusion is suppressed. In addition, the undesirable effect of Ag migration can be reduced.

  Note that x and y in the general formula indicate the ratios of Ae and Ag that can be substituted with the Ln and M elements, respectively, and can be real numbers that satisfy 0 ≦ x <1 and 0 <y <0.15. When x and y are in this range, the perovskite crystal structure can be kept stable even in a high temperature region of, for example, about 600 ° C., and Ag migration can be suppressed. Further, it is possible to form a fuel cell material provided with electrical conductivity, catalytic activity, and the like inherent in Ag.

  X indicating the replaceable ratio of Ae may be 0. That is, the A site may be occupied only by the lanthanoid element. However, for example, it is preferable to include Ae in consideration of the elements of the B site. In this case, x is suitably in the range of about 0 or more and 0.6 or less, preferably 0.1 or more and 0.5 or less. The value of x is not less than 0.1 and not more than 0.3, for example, in the vicinity of 0.25 (for example, 0.25 ± 0.02) although it cannot be generally stated because it depends on the combination of elements at the A site and the B site. ), It is more preferable because the A site can be an A site ordered perovskite structure that is ordered and occupied by two or more ions (Ln and Ae) in a ratio of about 3: 1 to 4: 1. In the case where such Ae is Sr, for example, those in which x is in the range of about 0.3 to 0.5 can be a preferred form.

  Y indicating the substitutable ratio of Ag can be preferably in the range of more than 0 and less than 0.15. That is, Ag occupies a part of the B site as an essential element. Such y is preferable because if it exceeds 0, an effect such as electric conductivity and catalytic activity of Ag can be imparted to the fuel cell material even if it is very slight. In order to make this action clearer, y is preferably 0.0001 or more, and more preferably 0.001 or more. However, if the proportion of Ag increases too much, it becomes difficult to stably keep Ag in the crystal structure under a high-temperature electric field, so y is preferably less than 0.15, and more preferably 0. More preferably, it is 10 or less, for example 0.05 or less.

Δ is a value determined so as to satisfy the charge neutrality condition in the perovskite oxide. In other words, as described above, this perovskite oxide can be understood to indicate the amount of oxygen defects in the simple perovskite structure represented by ABO ₃ by the δ value. Such δ varies depending on the type of atom substituting a part of the perovskite structure, the substitution ratio, environmental conditions, and the like, so that it is difficult to display accurately. For this reason, δ, which is a variable for determining the number of oxygen atoms, typically employs a positive number not exceeding 1 (0 ≦ δ <1) and is expressed as (3-δ). However, in this specification, there are cases where δ is omitted for convenience (for example, Table 1 below), but in such a case, different compounds are not shown. That is, (3-δ) in the above general formula is not intended to limit the technical scope of the present invention.

  The perovskite oxide represented by the above general formula exhibits a relatively high electrical conductivity from room temperature to a high temperature range even though it is an oxide. Moreover, since Ag is contained in the crystal structure, it can be excellent in electrical conductivity and catalytic activity as compared with a conventional perovskite oxide not containing Ag. And since it is stable at high temperature, the worry of Ag migration is prevented even in a high temperature environment. That is, for example, even when such a fuel cell material is in contact with an insulator, Ag is prevented from diffusing into the insulator to reduce or lose the insulation of the insulator. Can do.

  The form of the perovskite oxide is not particularly limited. Typically, a powder form is preferably used because it is easy to handle. The form of the powder is typically substantially spherical, but is not limited to a so-called true spherical shape. Other than the spherical shape, for example, a flake shape, a crushed shape, a granulated shape, or an irregular shape may be used. Further, the particle size of the perovskite oxide powder is not particularly limited, and those having an average particle size of 20 μm or less are suitable, preferably 0.01 μm or more and 10 μm, more preferably Is 0.3 μm or more and 5 μm or less, for example, 2 μm ± 1 μm. Note that the average particle diameter here is a particle diameter (50% volume average particle diameter; hereinafter abbreviated as D50) in the particle size distribution measured by a particle size distribution measuring apparatus based on a laser scattering / diffraction method. It may also be.) Further, a molded body in which such a powdery perovskite oxide is molded may be used.

  Further, it goes without saying that the fuel cell material disclosed herein may contain components other than the perovskite oxide and unavoidable impurities as long as the object of the present invention is not impaired. Preferably, it is a single phase of a perovskite oxide represented by the above general formula. However, for example, in the preparation of such a fuel cell material, an unintended impurity phase may be sufficiently contained. Even in such a case, if such a material is mainly composed of a perovskite oxide represented by the above general formula, such a material can be included in the fuel cell material of the present invention. Although not limited, as a rough guide, when the entire fuel cell material is 100% by mass, for example, the mass ratio is 10% by mass or less, typically 5% by mass or less, for example 3% by mass. % Of other components (such as other perovskite type oxides).

[Method for preparing fuel cell material]
The fuel cell material disclosed herein is not particularly limited in its preparation method, and can be prepared according to a known preparation method for oxide materials.
Specifically, for example, as a method for producing a powdered perovskite oxide, a dry method, a wet method, or the like is known as a representative method.
The dry method is, for example, a method in which raw material compounds as constituents of a powdered perovskite oxide are dry-mixed in a stoichiometric composition and calcined. Such a raw material compound may be, for example, a compound of each element of Ln, Ae, M and Ag represented by the above general formula (for example, oxide, carbonate, nitrate, etc.), or a compound of a plurality of elements It may be. Alternatively, the adjustment can be made even if the main perovskite oxide powder and the Ag powder are combined (may be alloyed) by a mechanical alloying technique.

  The wet method is a method in which a mixed solution containing all the constituents of the perovskite oxide in a stoichiometric ratio is prepared, and the target perovskite oxide is precipitated from the mixed solution. Typically, there are a coprecipitation method and a spray method. In the coprecipitation method, a precipitate-forming solution is added to a mixed solution containing all components in a stoichiometric ratio to coprecipitate a hydroxide containing the target metal element in a stoichiometric ratio. Is a method of drying and calcining. The spraying method is a method of spraying a mixed solution containing all of the constituent components in a stoichiometric ratio by using an atomizer or the like, and drying and calcining the liquid droplets in a droplet state. Examples of the raw material compound used in the wet method include oxides, hydroxides, carbonates, nitrates, acetates, formates and oxalates of each element of Ln, Ae, M and Ag represented by the above general formula. However, it is not limited to these.

[How to use fuel cell materials]
In addition, since the fuel cell material can be composed of an oxide that can have ionic / electron mixed conductivity as described above, it can be preferably used to form a constituent member constituting the fuel cell. . As such a constituent member, a constituent member of an SOFC that operates at the highest temperature among fuel cells can be preferably considered, and specific examples thereof include an SOFC air electrode, a current collector, and the like.

  That is, the fuel cell material disclosed herein exhibits good electrical conductivity and ionic conductivity at high temperatures, and has a thermal expansion coefficient close to that of a zirconia-based oxide that is a general SOFC electrolyte, Because of its low reactivity, it is preferably used as a material constituting the SOFC air electrode. In particular, the fuel cell material disclosed herein can exhibit a relatively large oxygen non-stoichiometry under high oxygen partial pressure conditions, which are the operating conditions of the SOFC air electrode. Therefore, if such a fuel cell material is used for the air electrode, the electrode reaction occurs not only at the three-phase interface where the electrode (air electrode) / electrolyte / gas phase (oxygen-containing gas) contacts but also at the surface of the electrode (air electrode) itself. Therefore, it is preferable because a relatively high electrode activity can be exhibited even in a temperature range of about 600 ° C., for example. In addition, Ag is stably contained in the crystal structure, and even when the SOFC is operated in a temperature range of about 600 ° C., the electrocatalytic activity is hardly lowered over a long period of time, and the deterioration of the SOFC cell performance is suppressed. It is also preferable in terms of obtaining.

  In addition, the current collector that connects the SOFC single cells also serves as a partition wall that separates the SOFC fuel electrode and air electrode, so that in addition to high electrical conductivity, an oxidizing atmosphere at high temperature and It is required to have resistance against both reducing atmospheres. As such a material for the SOFC current collector, the fuel cell material disclosed herein can be preferably used. In addition, the current collector referred to in this specification is a component member also called an interconnector, a separator, etc. in the SOFC. For example, the air electrode of one cell and the fuel electrode of the other cell are electrically joined. Or a member that electrically connects one air electrode or fuel electrode to another component.

According to such a fuel cell material, various fuel cell components can be manufactured according to a known method. For example, the above-described fuel cell material can be formed as it is alone or together with a sintering aid or the like into a desired form and fired to produce a constituent member of the target fuel cell.
In such molding, for example, a powdery fuel cell material may be prepared and used in the form of a paste (including ink, slurry, etc.) dispersed in an organic medium. Any organic medium may be used as long as it can disperse the fuel cell material disclosed herein well, and those used in conventional pastes of this type can be used without particular limitation. Typically, a mixture of a vehicle and an organic solvent for viscosity adjustment can be considered. As such an organic solvent, for example, a high boiling point organic solvent such as ethylene glycol and diethylene glycol derivatives (glycol ether solvents), toluene, xylene, butyl carbitol (BC), terpineol, or the like may be used alone or in combination. it can. In addition, the vehicle can contain various resin components as an organic binder. Such a resin component is not limited as long as it can impart a good viscosity and film-forming ability (for example, including printability and adhesion to a substrate) in preparing a paste. What is used for can be used without a restriction | limiting in particular. Examples thereof include those mainly composed of acrylic resin, epoxy resin, phenol resin, alkyd resin, cellulosic polymer, polyvinyl alcohol, rosin resin and the like. Among these, it is particularly preferable that a cellulosic polymer such as ethyl cellulose is contained.

  The ratio of the organic medium can be appropriately adjusted according to the form of the constituent members of the fuel cell, the method employed for the molding thereof, and the like. For example, when an SOFC air electrode green sheet is formed by a method such as screen printing or a doctor blade method, the organic medium is the entire paste (that is, the total of the fuel cell material and the organic medium). The proportion of the slag may be about 5% by mass or more and 60% by mass or less, preferably 7% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 40% by mass or less. The organic binder contained in the vehicle is, for example, about 1% by mass to 15% by mass of the entire paste, preferably about 1% by mass to 10% by mass, and more preferably about 1% by mass to 7% by mass. The ratio is exemplified. With this configuration, for example, a powdered fuel cell material can be easily formed (coated) as a layered body (for example, a coating film) having a uniform thickness, and can be easily handled. It is preferable because it does not take a long time to remove the. In particular, an SOFC air electrode green sheet (an unfired molded body) that can be made thinner can be suitably formed.

In preparing the paste, for example, a known three-roll mill can be used for mixing the fuel cell material and the organic medium. The pasty fuel cell material can be easily supplied to the desired position in the desired form in the form of coating or printing by adjusting the viscosity to an appropriate viscosity according to the desired application. Is possible. For example, it is possible to easily and suitably form a molded body for uses such as an SOFC air electrode whose dimensions are controlled with extreme precision, and an interconnector having a complicated shape.
The fuel cell material disclosed herein can be formed into a molded body (for example, a pellet having a desired shape) by compression molding a powdery material into a predetermined form.

  The molded body of the fuel cell material prepared as described above can be fired in the same manner as a conventional component of this type. In this case, the firing temperature can be, for example, about 1000 ° C. to 1400 ° C. However, when such firing is performed simultaneously with firing of other constituent members, the firing temperature can be appropriately changed. Thereby, for example, a desired fuel cell component such as an SOFC air electrode or an interconnector can be produced.

[Embodiment 1]
The solid oxide fuel cell (SOFC) system 1 in such an embodiment includes a plurality of anode-supported cylindrical SOFC single cells 10 shown in FIG. This single cell 10 has a dense layered solid electrolyte 22 made of an oxide ion conductor and a porous structure air electrode (cathode) on the outer surface of a cylindrical and porous fuel electrode (anode) 26 in this order. 24 is formed. During operation of the SOFC, the fuel gas (typically hydrogen (H ₂ )) passes through the fuel electrode 26 to the surface of the solid electrolyte 22 on the fuel electrode 26 side, and oxygen (typically hydrogen (H ₂ )) passes through the air electrode 24 to the surface of the solid electrolyte 22 on the air electrode 24 side. O ₂ ) containing gases (typically air) are each supplied. In a typical operation, O ₂ gas of oxygen (O ₂₎ containing gas is reduced by the air electrode 24 O ₂ ^- become anions, through the solid electrolyte to move to the fuel electrode 26, the H ₂ gas fuel Oxidize. And with this oxidation reaction, electric energy is generated.

Here, as the material constituting the air electrode 24, the fuel cell material disclosed herein can be used. Specific examples of such fuel cell materials include (LaSr) (MnAg) O ₃ and (LaCa) (MnAg) O _3, and lanthanum manganate (LaMnO ₃ ) -based perovskite in which Ag is dissolved. Type oxides, lanthanum cobaltite (LaCoO ₃ ) based on solid solution of Ag, represented by La (CoAg) O ₃ , (LaSr) (CoAg) O ₃ , (LaSr) (CoFeAg) O _3, etc. Examples thereof include perovskite oxides, and those made of lanthanum titanate (LaTiO ₃ ) -based perovskite oxides in which Ag is solid solution, such as (LaSr) (TiFeAg) O ₃ . It should be noted that the chemical formulas listed here indicate combinations of elements constituting such oxides, as are conventionally used by those skilled in the art, and do not indicate actual compositions of fuel cell materials. Absent.
Examples of the solid electrolyte 22 include those made of 8% yttria stabilized zirconia (8YSZ) or lanthanum gallate (LaGaO ₃ ). As an example of the fuel electrode 26, an electrode made of cermet of nickel (Ni) and YSZ is exemplified. Although not disclosed in FIG. 1, a reaction preventing layer may be provided between the air electrode 24 and the solid electrolyte 22 for the purpose of preventing these reactions. Examples of such a reaction preventing layer include those made of gadolinia doped ceria (GDC).

In addition, for example, in the case of the SOFC system 1 having a configuration in which cylindrical single cells 10 are connected in series via an interconnector 30 as shown in FIG. 1, the interconnector 30 is disclosed herein. The fuel cell material can be used. In order to construct the SOFC system 1, a plurality of cylindrical single cells 10 are prepared in advance, and the interconnector material prepared by pasting the fuel cell material into a paste is applied to a predetermined region on the peripheral side surface of the single cell 10. It can manufacture by apply | coating and connecting and baking the single cells 10 through this interconnector material.
By producing the SOFC air electrode 24, the interconnector 30 and the like using such a fuel cell material, it is possible to form a fuel cell constituent member excellent in ion-electron mixed conductivity. Furthermore, even when exposed to an operating environment of SOFC of about 600 to 900 ° C., for example, Ag is prevented from diffusing between the fuel cell constituent member and other members, and for example, an increase in the overvoltage of the air electrode is prolonged. Therefore, the SOFC system 1 having excellent electrode activity can be realized. Moreover, since migration of Ag from the interconnector 30 is prevented, the insulation of an insulating member (for example, a gas pipe (not shown) connected to the air electrode 24 or an external insulating member) in the SOFC system 1 is impaired. Thus, a high-performance SOFC system 1 having excellent power generation characteristics over a long period of time can be realized.

[Embodiment 2]
The solid oxide fuel cell (SOFC) system in such an embodiment includes an SOFC stack cell 100. FIG. 2 schematically shows an exploded perspective view of one embodiment of the stack cell 100. The stack cell 100 is configured as a stack in which a plurality of SOFCs (single cells) 10A and 10B are stacked via an interconnector 30. The unit cells 10A and 10B have a sandwich structure in which both surfaces of a layered solid electrolyte 22 are sandwiched between a layered fuel electrode (anode) 24 and an air electrode (cathode) 26, respectively. The interconnector 30A disposed in the center of the drawing is sandwiched between two single cells 10A and 10B, one cell facing surface 32 faces (adjacent) the air electrode 24 of the cell 10A, and the other cell. The facing surface 34 faces (adjacent) the fuel electrode 26 of the cell 10B. The air electrode 24 and the interconnector 30 are made of the fuel cell material disclosed herein. A plurality of grooves are formed in the cell facing surface 32 of the interconnector 30 to form an air flow path 33 through which the supplied oxygen-containing gas (typically air) flows. Similarly, a plurality of grooves are also formed in the opposite cell facing surface 34 to constitute a fuel gas passage 35 through which the supplied fuel gas (typically H ₂ gas) flows. In the interconnector 30 of this form, the air flow path 33 and the fuel gas flow path 35 are typically formed so as to be orthogonal to each other. In a typical operation, O ₂ gas of oxygen (O ₂₎ containing gas is reduced by the air electrode 24 O ₂ ^- become anions, through the solid electrolyte to move to the fuel electrode 26, the H ₂ gas fuel Oxidize. And with this oxidation reaction, electric energy is generated.
The manufacturing method of the SOFC system described above may be in accordance with a conventionally known manufacturing method and does not require special processing, and thus detailed description thereof is omitted.

  Hereinafter, some test examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in the test examples.

[Preparation of SOFC for evaluation]
[Production of SOFC half-cell]
As fuel electrode materials, 8 mol% yttria-stabilized zirconia (8 mol% Y ₂ O ₃ —ZrO ₂ , hereinafter referred to as “8YSZ”) powder having an average particle diameter of 1 μm and nickel oxide (NiO) powder having an average particle diameter of 1 μm are used. NiO: 8YSZ = 60: 40 was mixed to obtain a mixed powder. This mixed powder, binder (polyvinyl butyral; PVB), pore former (carbon particles, average particle size: about 5 μm), and plasticizer (dibutyl phthalate) in a mass ratio of 76: 11: 7: 6 Were mixed in and dispersed in a solvent to prepare a paste-like composition for forming a fuel electrode. In this embodiment, a solvent in which 2-propanol and toluene are mixed at a mass ratio of 4: 1 is used as the solvent. Next, this fuel electrode forming composition was applied on a carrier sheet in a sheet form by a doctor blade method and dried to form a fuel electrode green sheet having a thickness of 0.8 mm.

Next, an 8YSZ powder having an average particle size of 0.5 μm, a binder (ethylcellulose; EC), and a solvent (α-terpineol; TE) were kneaded at a mass ratio of 65: 4: 31 to obtain a paste-like material. A composition for forming a solid electrolyte layer was prepared. A solid electrolyte layer green sheet having a thickness of 10 μm was formed by supplying the sheet on the fuel electrode green sheet by a screen printing method. Further, gadolinium-doped ceria (Ce _0.9 Gd _0.1 O ₂ , hereinafter referred to as “GDC”) powder having an average particle size of 0.5 μm, a binder (EC), a solvent (α-terpineol; TE), Was kneaded at a mass ratio of 65: 4: 31 to prepare a paste-like composition for a reaction preventing layer. This was supplied in a sheet form on the solid electrolyte layer green sheet by a screen printing method, thereby forming a solid electrolyte layer green sheet having a thickness of 5 μm.
The laminated green sheet thus prepared was co-fired at 1400 ° C. to obtain a SOFC half cell.

[Formation of air electrode]
Next, fuel cell materials containing Ag components; A0 to A5, B1 to B6, C1 to C6, D1 to D6, and E1 to E6 were prepared as SOFC air electrode materials. That is, for the perovskite oxides indicated by A to E in Table 1, Ag in the ratio shown in the column of “Ag component (y)” in Table 2 is mixed (A) or (B to E) is solid. A fuel cell material was prepared by melting. Specifically, each fuel cell material was prepared as follows.

A: Mixed Fuel cell materials A0 to A5 are composed of y mol of Ag powder as an Ag component shown in Table 2 with respect to 1 mol of powdery perovskite oxide (LSCF) having the composition shown by A in Table 1. It prepared by weighing each in the ratio which becomes. The average particle size of the LSCF powder used for the preparation was 1 μm, and the average particle size of the Ag powder was 0.2 μm. The fuel cell material A0 is an LSCF simple substance in which the ratio of the Ag component is “0” and no Ag component is contained. In addition, the fuel cell material No. In the column of “Ag component (y)” regarding A0 to A5, “*” indicating that the standard of the ratio of the Ag component is different from B1 to E6 described later is attached.
The perovskite oxide powder and Ag powder are kneaded together with a binder (ethyl cellulose; EC) and a solvent (α-terpineol; TE) at a mass ratio of 65: 4: 31 to form a paste-like air electrode. Compositions A0 to A5 were prepared. This was supplied in the form of a sheet by the screen printing method on the SOFC half cell prepared above to form an air electrode layer green sheet having a thickness of 30 μm, and fired at 1100 ° C. to form an air electrode. Thereby, SOFC cells A0 to A5 for evaluation were obtained. Hereinafter, this evaluation cell is simply referred to as “cell A0” or the like in correspondence with the fuel cell material used. In addition, the composition for air electrode formation prepared here was used also for evaluation of "Ag migration resistance" shown below.

B to E: Solid solution (Mechanochemical treatment)
Fuel cell materials B1 to B6, C1 to C6, D1 to D6, and E1 to E6 were prepared by the following procedure. That is, first, the perovskite oxides shown by B to E in Table 1 have a composition in which the transition metal at the B site is substituted with Ag in the ratio shown in the column “Ag component (y)” in Table 2. The raw material powder was blended at a stoichiometric ratio. That is, according to the ratio (y) of the Ag component, each raw material powder is weighed and mixed so that the composition of the perovskite oxide shown in the column of “Fuel cell material” in Table 1 is obtained. Prepared. As the raw material powder, an oxide of each constituent element of the target perovskite oxide was used. Next, the mixed powder is put into a dry particle compounding device (Nosoluta 130 manufactured by Hosokawa Micron Corporation), and dry mixing is performed by mechanochemical treatment (solution treatment) for 10 to 20 hours at a dispersion power of 3 kW. It was. The average particle size of the LSCF powder used for the preparation was 1 μm, the average particle size of the Ag powder was 0.2 μm, and the average particle size of the obtained fuel cell material was about 1 μm. The powdered product thus obtained was used as a fuel cell material.

  Next, SOFC cells for evaluation were produced using the fuel cell materials B1 to B6, C1 to C6, D1 to D6, and E1 to E6 prepared above as the air electrode material. That is, by pasting such a fuel cell material, a binder (ethylcellulose; EC), and a solvent (α-terpineol; TE) at a mass ratio of 65: 4: 31, a paste-like composition for forming an air electrode is obtained. A product was prepared. This was supplied in the form of a sheet by the screen printing method on the SOFC half cell prepared above to form an air electrode layer green sheet having a thickness of 30 μm, and fired at 1100 ° C. to form an air electrode. Thereby, SOFC cells B1 to B6, C1 to C6, D1 to D6 and E1 to E6 for evaluation were obtained. Hereinafter, this evaluation cell is simply referred to as “cell B0” or the like, corresponding to the fuel cell material used. The air electrode forming composition prepared here was also used for evaluation of “Ag migration resistance” shown below.

The composition of the fuel cell material obtained by the solution treatment was examined using a fluorescent X-ray analyzer (manufactured by Rigaku Corporation, ZSX100e). The charged composition (composition of the target fuel cell material) It was confirmed that there was no deviation in the composition of the obtained product.
Further, the crystal structures of all the obtained fuel cell materials were examined by X-ray diffraction analysis. For reference, X-ray diffraction patterns of the fuel cell material A4 obtained by the mixing treatment and the fuel cell material B4 obtained by the solution treatment are shown in FIG.
As a result, a peak attributed to the perovskite oxide and a peak attributed to Ag were confirmed in the fuel cell material (for example, A4) obtained by the mixing treatment. On the other hand, for the fuel cell material (for example, B4) obtained by mechanochemical treatment, only the peak attributed to the target perovskite oxide is seen in the solid solution X-ray diffraction pattern, and the peak of Ag alone is seen. It was confirmed that Ag was incorporated in the crystal structure of the perovskite oxide.

[Ag migration resistance evaluation]
Migration of Ag contained in these fuel cell materials using the composition for forming an air electrode containing the fuel cell materials A0 to A5, B1 to B6, C1 to C6, D1 to D6 and E1 to E6 prepared above. Sexuality was evaluated. That is, each air electrode forming composition was applied to an insulating substrate (gadolinium-doped ceria: GDC) with a thickness of 50 μm and baked at 700 to 900 ° C. to form an evaluation air electrode. For this air electrode for evaluation, the electrical resistance of the air electrode when a voltage of 50 V is applied in air at 700 ° C. is measured, and whether conduction can be obtained within 5 minutes (ie, insulation within 5 minutes) Whether the substrate is short-circuited) was evaluated for Ag migration resistance. The result is shown in the column of “Ag migration resistance” in Table 2. The evaluation symbols shown in Table 2 mean the following contents.
X: Short circuit time is less than 5 minutes, and Ag ion moves easily in an air electrode.
○: Short circuit cannot be confirmed over 5 minutes, and movement of Ag ions is suppressed in the air electrode.

[Evaluation]
As shown in Table 2, the air electrode formed using the fuel cell material A0 is composed of LSCF that does not contain an Ag component, and therefore does not short-circuit the insulating substrate even when placed in an electric field. It was. On the other hand, when the air electrode is formed using the fuel cell materials A1 to A5 obtained by mixing the LSCF and the Ag powder, the insulating substrate is formed by the electric field in a short time regardless of the ratio of the mixed Ag powder. It was confirmed that the Ag component could be easily diffused in the insulating substrate due to a short circuit.
On the other hand, for the air electrode formed using the fuel cell material in which the Ag component is solid-solved in the crystal structure of the perovskite oxide, the introduction ratio of the Ag component is less than 0.15 in molar ratio ( That is, fuel cell materials B1 to B5, C1 to C5, D1 to D5, and E1 to E5), and the insulating substrate was not short-circuited even in an electric field. In other words, it was found that the Ag component was introduced into the crystal structure of the perovskite oxide by the solution treatment, so that the Ag component was retained in the crystal structure even in an electric field, and diffusion into the insulating substrate was suppressed. It was also confirmed that the effect of suppressing the diffusion of the Ag component does not greatly depend on the composition of the perovskite oxide mainly constituting the air electrode. However, it has been found that when the introduction ratio of the Ag component is 0.15 or more in terms of molar ratio, Ag cannot be stably retained in the crystal structure, and the Ag component tends to diffuse.

[Cell performance evaluation]
The cells A0 to A5, B1 to B6, C1 to C6, D1 to D6, and E1 to E6 obtained above were evaluated for power generation performance when operated at 600 ° C. That is, for each evaluation cell, in an environment of 600 ° C., the output of the evaluation cell was measured when hydrogen (H ₂ ) was supplied to the air electrode at 50 ml / min and Air was supplied to the air electrode at 100 ml / min. The output (power density) per unit area of the cell was calculated. The results are shown in the column of “Cell performance” in Table 2.

About cell performance, it has confirmed from the comparison of cell A0-A5, B1-B6 that it exists in the tendency which becomes high, so that the ratio of the Ag component contained in a fuel cell material increases. That is, it has been confirmed that the Ag component contained in the air electrode enhances the conductivity and catalytic function of the air electrode, and the cell output is improved as the ratio increases. However, it was confirmed that the effect of improving the cell performance stopped when the ratio of the Ag component reached about 0.15 in terms of molar ratio. In addition, there is no difference in cell performance between the cells A1 to A5 using the fuel cell material mixed with the Ag component and the cells B1 to B5 using the fuel cell material in which the Ag component is solidified, It was also found that the presence form of Ag does not affect the cell performance.
In addition, the same tendency was seen about the cells C1-C6, D1-D6, and E1-E6 that cell performance improved, so that the ratio of the Ag component contained in a fuel cell material increased. However, it has been shown that the cell performance itself greatly depends on the composition of the perovskite oxide mainly constituting the air electrode, and the degree of improvement in cell performance by the Ag component varies depending on the composition.

[Evaluation of cell deterioration rate]
Moreover, the cell A0 to A5, B1 to B6, C1 to C6, D1 to D6, and E1 to E6 obtained above were evaluated for the cell deterioration rate when operated at 600 ° C. That is, for each evaluation cell, hydrogen (H ₂ ) is supplied to the air electrode and Air to the air electrode so that power is generated in a constant current mode with a reference output of 0.5 A / cm ^{2 in} an environment of 600 ° C. Supplied. And the output of each cell for evaluation before and after performing the electric power generation in this constant current mode for 100 hours was measured, and the reduction rate is shown in Table 2 as the deterioration rate.

The cell deterioration rate generally showed the same tendency as the Ag migration resistance. That is, the cell deterioration rate was suppressed to a low value of 0.4% or less for the cells having good (A) Ag migration resistance characteristics. However, for cells with poor migration resistance (x), the cell deterioration rate is 0.5% or more, and the deterioration rate can take a high value rapidly as the proportion of the Ag component increases. I understood.
From the results of the cells B1 to B6, C1 to C6, D1 to D6, and E1 to E6, when the ratio of the Ag component reaches 0.15 in terms of molar ratio, the cell deterioration rate decreases from 0.4% or less. It was found that it rose rapidly to over 3%. This suggests that Ag is stably dissolved in the perovskite crystal structure in the SOFC operating environment at a molar ratio of less than about 0.15. It has been confirmed that the cell deterioration rate itself does not greatly depend on the composition of the perovskite oxide mainly constituting the air electrode.

From the above, it has been confirmed that the fuel cell material disclosed herein can suppress diffusion of Ag contained in the crystal structure even when placed in a high-temperature electric field. It has also been confirmed that by forming an SOFC air electrode using such a fuel cell material, an SOFC having excellent output characteristics and durability can be realized. Such a fuel cell material having excellent ionic / electron mixed conductivity is suitable for constituting the SOFC air electrode, for example, a current collector disposed between the air electrode and the interconnector. Can also be used preferably.
As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

1 SOFC system 10, 10A, 10B Single cell 20 Junction 22 Solid electrolyte 24 Air electrode (cathode)
26 Fuel electrode (anode)
30, 30A, 30B Interconnectors 32, 34 Cell facing surface 33 Air flow path 35 Fuel gas flow path 100 Stack cell

Claims (7)

It has a perovskite crystal structure,
A fuel cell material comprising an oxide in which Ag is dissolved in the crystal structure. The oxide has the following general formula:
(Ln _1-x , Ae _x ) (M _1-y Ag _y ) O _3-δ
(Wherein Ln is one or more elements selected from lanthanoids, Ae is one or more elements selected from the group consisting of Ca, Sr and Ba, and M is Co , Mn, Cr, Cu, Fe, Ni, and Ti, one or more elements selected from the group consisting of Ti, and x and y are 0 ≦ x <1, 0 <y <0.15, respectively. And δ is a value determined to satisfy the charge neutrality condition)
The fuel cell material according to claim 1, which is represented by: The fuel cell material according to claim 1, wherein the M is Co or Fe or both.   The fuel cell material according to claim 1, wherein y satisfies 0.0001 ≦ y ≦ 0.1.   A fuel cell constituent member comprising the fuel cell material according to claim 1.   It is an air electrode of a solid oxide fuel cell, Comprising: The air electrode which consists of a fuel cell structural member of Claim 5.   A solid oxide fuel cell comprising the air electrode according to claim 6.

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