JP2016110935A - Electrode material for solid oxide fuel cell, and utilization thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode material for SOFC which enables the enhancement in performance of an electrode such as an air electrode of SOFC of a type working at a low temperature (e.g. about 600-700°C), for example.SOLUTION: An electrode material used for forming an electrode of a solid oxide fuel cell is provided according to the present invention. The electrode material comprises: complex particles in which a first oxide having a perovskite type crystal structure and expressed by the general formula, (LnSr)BO, and a second oxide expressed by the general formula, XNiOare bound to each other by a mechanical method. In the formulas, Ln represents at least one lanthanoid, B represents at least one element selected from Ni, Co, Mn, Cr, Cu, Fe and Ti, 0.1≤x≤0.9, and δ is a value determined so as to satisfy a charge neutral condition; X includes at least one element selected from La, Pr and Nd, and δ' is a value determined so as to satisfy a charge neutral condition.SELECTED DRAWING: Figure 1

Description

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

A solid oxide fuel cell (SOFC: Solid Oxide Fuel Cell, hereinafter simply referred to as “SOFC”) has a high power generation efficiency and a low environmental load among various types of fuel cells. It has the advantage that 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 air electrode to become an O ^2- anion, passes through the solid electrolyte, and generates electric energy as the H ₂ gas fuel is oxidized at the fuel electrode. Is generated.

  Such SOFCs have been operated at a high temperature of 800 ° C. or higher (typically about 800 ° C. to 1000 ° C.) conventionally, but in recent years, such operations have 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 to 700 ° C. For a low-temperature operation type SOFC, for example, an air electrode is formed using a so-called electron-oxygen ion mixed conductive material exhibiting electronic conductivity and oxygen ion conductivity, so that an electrode / electrolyte / gas phase is formed. It is expected that the electrode reaction is advanced not only on the three-phase interface with which the electrode contacts but also on the surface of the electrode (air electrode) to enhance the electrode activity. However, when the SOFC is operated at a low temperature, the overvoltage at the air electrode is increased, resulting in a problem that cell performance (for example, power density) is lowered.

  In order to compensate for the deterioration in cell performance due to such overvoltage, for example, it has been studied to improve the performance of the electrode material constituting the air electrode. For example, it has been proposed to increase the reaction field composed of the three-phase interface and the electrode surface by miniaturizing the electrode material constituting the air electrode and increasing the specific surface area. According to such a method, although the reaction field can be increased, there is a problem that the interface resistance increases and the cell performance decreases.

  The present invention has been created to solve the above-described conventional problems, and its purpose is to improve the performance of electrodes such as air electrodes of SOFCs that operate at low temperatures (for example, about 600 ° C. to 700 ° C.). It is to provide an electrode material for SOFC that can be made to be used. Another object of the present invention is to provide an air electrode using such an electrode material and a SOFC equipped with such an air electrode.

In order to achieve the above object, the present invention provides an electrode material used for forming an electrode of a solid oxide fuel cell. The electrode material has a perovskite crystal structure, the general _{formula: (Ln 1-x Sr x} ) BO 3-δ; a first oxide represented by the general _formula: X 2 NiO _{4-δ '} And a second oxide represented by: And it is characterized by including the composite particle | grains by which the said 2nd oxide was joined to the surface of the said 1st oxide with the mechanical method. In the above general formula, Ln represents at least one lanthanoid element, B represents at least one element selected from Ni, Co, Mn, Cr, Cu, Fe and Ti, and 0.1 ≦ x ≦ 0.9, and δ is a value determined to satisfy the charge neutrality condition. X includes at least one element selected from La, Pr, and Nd, and δ ′ is a value determined to satisfy the charge neutrality condition.

  The perovskite-type first oxide and the second oxide are both electron-oxygen ion mixed conductors. However, due to the difference in crystal structure, it is considered that the expression mechanisms of the oxygen ion conductivity are different from each other. The present inventors tried to improve the characteristics by compounding these different types of oxides, and by combining these oxides by a mechanical method while maintaining the crystal structure of each other, these oxidations were performed. It was found that the contact resistance at the interface of the object can be reduced and the oxygen ion conductivity can be improved. The present invention has been created based on such knowledge. Such an electrode material can be suitably used as, for example, an SOFC air electrode forming material.

  In a preferred embodiment of the electrode material disclosed herein, the composite particles are obtained by dry-mixing the first particles containing the first oxide and the second particles containing the second oxide by a mechanical method. It is characterized by being formed. According to such dry mixing, the second particles can be disposed (coated) in a suitable state on the surface of the first particles by the collision energy between the particles. Thereby, an electrode material having further excellent oxygen ion conductivity is provided.

  In a preferred embodiment of the electrode material disclosed herein, the actual value S of the specific surface area of the composite particles and the sum of the specific surface areas of the first particles and the second particles used to form the composite particles Based on the theoretical specific surface area S ′ defined and the electrode resistance R measured by the AC impedance method for an electrode having a thickness of 10 μm or more and 100 μm or less formed using the composite particles, the following formula: P = R × The parameter P defined by S × (S / S ′); satisfies P ≦ 1.4. Thereby, the electronic conductivity of this electrode material and oxygen ion conductivity can be reconciled in good balance.

  In a preferred embodiment of the material disclosed herein, the ratio of the second oxide in the total of the first oxide and the second oxide is more than 0% by mass and 50% by mass or less. It is characterized by being. Such a blending ratio is preferable because the resistance at the interface between the first oxide and the second oxide can be suitably suppressed.

In another aspect, the invention disclosed herein provides a SOFC component. Such constituent members are characterized by being made of any of the electrode materials described above.
According to such a configuration, characteristics such as ionic conductivity and oxygen conductivity of the constituent member can be improved due to the perovskite crystal structure having the above characteristics. Therefore, for example, by configuring the SOFC air electrode with such a component, the SOFC electrode reaction resistance can be reduced, and the power generation performance can be improved. The electrode material having such characteristics can be preferably used for constituting the SOFC air electrode, and can also be suitably used as a current collector for the air electrode, for example. Therefore, according to the invention disclosed herein, components such as an air electrode and a current collector that can realize the above-described excellent SOFC performance are provided. As a result, the invention disclosed herein can provide an SOFC that can maintain excellent cell performance over a long period of time.

1 is a cross-sectional view schematically showing an anode-supported SOFC according to an embodiment of the present invention.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  The electrode material disclosed here includes the first oxide and the second oxide. And it is characterized by including the composite particle | grains by which the said 2nd oxide was joined to the surface of the 1st oxide with the mechanical method. In addition, about the content, composition, etc. of other components other than this composite particle, it can adjust in light of various standards, unless it deviates from the objective of this invention.

(First oxide)
In the technology disclosed herein, as the first oxide having a perovskite crystal structure, various oxides represented by the general formula: (Ln _1-x Sr _x ) BO _3-δ ; Can do.
Here, in the above formula, Ln is an element occupying the “A site” in the perovskite crystal structure together with strontium (Sr), and Ln is from lanthanum (Ln) of atomic number 57 to lutetium (Lu) of atomic number 71 Up to 15 lanthanoid elements. Any one of these lanthanoid elements may be contained alone, or Ln may be contained in combination of two or more. More specifically, the lanthanoid element is an element having a relatively large ionic radius, such as lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), and the like. Is preferred. Among them, it is preferable that the lanthanoid element is La or Sm, especially La because a more stable crystal structure can be formed. When the lanthanoid element includes an element other than La together with La, the ratio of La is preferably high. In addition, the ionic radius in this specification means the ionic radius of Shannon.

  In the formula, x represents the ratio of strontium (Sr) substituted for the lanthanoid (Ln) occupying the A site in the perovskite crystal structure as described above. x is suitably in the range of 0.1 or more and 0.9 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 0.5, for example, in the vicinity of 0.25 (for example, 0.25 ± 0) although it cannot be generally stated because it depends on the combination of elements at the A site and the B site described later. .02), 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 Sr) in a ratio of approximately 3: 1 to 4: 1. .

  “B” in the above general formula is an element occupying the “B site” in the perovskite crystal structure, and is nickel (Ni), cobalt (Co), manganese (Mn), chromium (Cr), copper ( It may be at least one element selected from the group consisting of Cu), iron (Fe), and titanium (Ti). Of these, any one of Co, Mn, Ni and Fe, or a combination of any two of these is preferable. In the case where the above element is included, since it has higher reactivity and oxygen ion conductivity than other perovskite oxides, it can exhibit excellent performance as an electrode even in a relatively low temperature region.

Δ is a value determined so as to satisfy the charge neutrality condition in the first oxide. That is, as described above, this first oxide can be understood to indicate the amount of oxygen defects in the 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, δ may be omitted for convenience, but in such a case, a different compound is not shown. That is, (3-δ) in the above general formula is not intended to limit the technical scope of the present invention.

Although not particularly limited, as a preferred embodiment of such a first oxide, for example, _{specifically, La 1-x Sr x (} Co 1-y Fe y) O 3-δ , La _1-x Sr _x CoO _3-δ , Sm _1-x Sr _x CoO _{3-δ, and the} like. Note that x and y in the formula satisfy 0.1 ≦ x ≦ 0.9 and 0 ≦ y ≦ 1. Note that these second oxides may contain other elements not exemplified above (for example, at least one transition metal element) without departing from the essence of the present invention.

  Since such a 1st oxide contains the transition metal element in B site, since the d electron of this transition metal ion is localized, it can show high electrical conductivity. In addition, since the transition metal is included in the B site, the valence of the transition metal ions may change depending on the surrounding environment. Can be formed. An oxygen defect can also be introduced by intentionally reducing the sum of the valences of the metal ions at the A site and the B site slightly from +6. The first oxide in which oxygen defects are introduced in this way can also be an oxygen ion conductor in which oxygen ions move quickly through the oxygen defects. At this time, the diffusion path of oxygen ions is along the <100> orientation of the crystal structure. That is, the electrode material containing such a first oxide can be a material useful as, for example, an SOFC electrode material (particularly an air electrode material).

(Second oxide)
In the technique disclosed here, a compound represented by the general formula: X ₂ NiO _{4-δ ′} can be targeted as the second oxide. This second oxide is a composite oxide having a so-called perovskite-like structure in which a perovskite crystal structure and a rock salt crystal structure are alternately stacked (in layers), and can exhibit ionic conductivity and electronic conductivity. However, in this second oxide, it is said that the interstitial oxygen introduced into the rock salt type crystal structure becomes the carrier rather than originating from oxygen defects, and the ionic conduction and electronic conduction are the rock salt layer, respectively. It can occur two-dimensionally with the perovskite layer. That is, the diffusion path of oxygen ions can be expanded in a two-dimensional plane. It can be said that such a second oxide is a completely different material from that of the first oxide, which has a different oxygen ion conduction mechanism.

As such a second oxide, specifically, an oxide represented by a general formula: X ₂ NiO _{4-δ ′} ; can be considered. Here, in the above formula, X can contain at least one element selected from La, Pr and Nd. Further, δ ′ is a value that is determined so as to satisfy the charge neutrality condition, and may be omitted hereinafter in the same manner as δ in the first oxide. A preferable embodiment of such a second oxide can be, for example, La ₂ NiO ₄ , La _1.6 Sr _0.4 NiO ₄ , Pr ₂ NiO ₄ , Nd ₂ NiO ₄ or the like. These second oxides may contain other elements not exemplified above (for example, at least one transition metal element, etc.) without departing from the essence of the present invention. Such a second oxide is derived from the crystal structure thereof, for example, the first oxide (for example, La _0.6 Sr _0.4 Fe _0.8 Co _0.2 O _3-δ or the like). ), A high oxygen ion conductivity can be exhibited particularly in a low temperature region (for example, 500 ° C. to 800 ° C.). Therefore, it can be particularly suitably used as an electrode material for SOFC driven in such a low temperature region (particularly about 600 ° C. to 700 ° C.).

Note that in this specification, in accordance with the custom in this technical field, an oxide such as La _0.6 Sr _0.4 Fe _0.8 Co _0.2 O _3-δ is hereinafter referred to as oxygen (O). There are cases in which the abbreviation is simply abbreviated as LSFC only by the initial letters of the constituent elements other than.

(Composite particles)
The first oxide and the second oxide described above are in the form of composite particles by bonding the second oxide to the surface of the first oxide by a mechanical method.
Unlike chemical methods such as chemical vapor deposition and liquid phase synthesis, the mechanical method combines the first oxide and the second oxide by applying mechanical force in the solid phase. To be integrated. Such mechanical force can be understood as, for example, force (energy) such as impact (collision), compression, shearing (grinding), or a mixture thereof. In the technique disclosed herein, the first oxide and the second oxide are not completely homogenized, but are in a composite particle (composite) state in which both are adhered and integrated. .

  Here, the presence form of the first oxide and the second oxide in the composite particle is not particularly limited. For example, a form in which a particulate first oxide is used as a core and at least a part of the surface thereof is covered with a second oxide in a layer form may be used. The second oxide may cover the entire surface of the first oxide. Alternatively, a part of the surface of the particulate first oxide may be covered with one or two or more island-like second oxides. As described above, in the composite particles disclosed herein, the first oxide and the second oxide exist integrally independently.

  For example, the first particles including the first oxide and the second particles including the second oxide are dry-mixed by a mechanical method, so that at least a part of the surface of the first particles is the second particles. A composite particle bonded in a covering form is a preferred embodiment. The form of the coating is not particularly limited, and for example, a part or the whole of the surface of the first particle may be coated with the second particle in a layer shape or an island shape. Such mechanical methods are typically integrated, for example, mechanical milling method in which hard balls are used for kneading with mechanical force, or mechanical force is applied using an anvil or other instrument. It can be realized by a large strain introducing method (also called a strong strain processing method). The conditions for the dry mixing by this mechanical method (for example, the processing speed, processing time, etc.) can be adjusted as appropriate so as to obtain a desired degree of compounding and a desired particle size. Here, the 1st particle and the 2nd particle may be produced from a raw material, for example, and may be purchased. Moreover, there is no restriction | limiting in particular also about a preparation method, For example, what was prepared using well-known methods, such as a dry method and a wet method, can be especially used without a restriction | limiting.

  The external shape of the composite particles obtained by the mechanical method 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 diameter (average particle diameter) of the composite particles is not particularly limited. The particle size of the composite particles is determined by the particle size of the oxide particles (first oxide powder and second oxide powder) used as a starting material in producing the composite particles, the mechanical method employed, and It can be adjusted according to the application time. The average particle diameter of the composite particles is, for example, appropriately 20 μm or less, preferably 0.01 μm or more and 10 μm or less, more preferably 0.3 μm or more and 5 μm or less, for example 2 μm ± 1 μm. . The average particle size of the composite particles referred to here is a particle size (50% volume average particle size; hereinafter referred to as an integrated value of 50% in a particle size distribution measured by a particle size distribution measuring apparatus based on a laser scattering / diffraction method. It may be abbreviated as D50).

  Further, the size and form of each of the first oxide (which is a part of the composite particle) and the second oxide (which is another part of the composite particle) constituting the composite particle are not particularly limited. For example, for the composite particles joined in such a manner that at least a part of the surface of the first particles is covered with the second particles, the average particle diameter of the first particles is suitably about 20 μm or less, preferably Is about 0.1 μm to 10 μm, more preferably about 1 μm to 8 μm, for example, about 2 μm to 5 μm. In addition, for example, the average particle diameter of the second particles covering the first particles is preferably smaller than the average particle diameter of the first particles, for example, about 10 μm or less is suitable, It is about 01 μm or more and 5 μm or less, more preferably about 0.05 μm or more and 3 μm or less, for example, about 0.1 μm or more and 1 μm or less. In addition, the average particle diameter about the 1st particle | grains and 2nd particle | grains here is the average measured by the laser diffraction and the scattering method similarly to the above about the particle | grains of about 100 nm or more according to the magnitude | size of the said particle | grain. The particle diameter can be adopted, and the average particle diameter measured by particle size distribution measurement based on the dynamic light scattering method (DLS) can be adopted for particles having a size of approximately 1 μm or less.

Further, the ratio of the first oxide and the second oxide constituting the composite particle is not particularly limited. The amount of the first oxide can be, for example, 50% by mass or more and 95% by mass or less when the entire composite particle is 100% by mass. Further, the amount of the second oxide can be, for example, 5% by mass or more and 50% by mass or less when the entire composite particle is 100% by mass.
In more detail, the average particle diameter and the ratio of the first oxide (for example, the first particle) and the second oxide (for example, the second particle) in the composite particle are not particularly limited. A more preferable example is that the form is adjusted so that the parameter P defined by (1) satisfies the relationship of P ≦ 1.4.

Here, the parameter P is a constituent factor related to the electrode formed using the composite particles, and is defined by the following equation.
P = R × S × (S / S ′)
Here, R represents the electrode resistance of the electrode formed using the composite particles, S represents the specific surface area of the composite particles, and S ′ represents the theoretical specific surface area of the composite particles. Here, the theoretical specific surface area S ′ is defined as the sum of the specific surface areas of the first particles and the second particles used to form the composite particles. And (S / S ') has shown the surface area reduction rate which is a ratio of the surface area reduced when the 1st particle and the 2nd particle were used for the mechanical method in a type | formula.

  Here, the electrode reaction in the air electrode of SOFC occurs at a so-called three-phase interface between the air electrode / electrolyte / gas phase. By using an oxygen ion mixed conductor as the air electrode material, a phenomenon that oxygen molecules are ionized from the oxygen-containing gas on the electrode surface and taken into the air electrode is observed. That is, the electrode reaction can proceed even on the air electrode surface. Therefore, in general, the air electrode material is configured to increase the specific surface area to increase the three-phase interface composed of the gas phase / air electrode / electrolyte interface, and to express relatively high electrode activity. . On the other hand, in the material disclosed here, the air electrode material is formed by combining finer particles (that is, the first particles and the second particles), and the specific surface area is intentionally reduced. Yes. Then, the interface state of the composite particles is adjusted to a more suitable state by the movement of oxygen ions, in other words, the microstructure of the particle interface in the electrode material is optimized so that the oxygen ions can move more smoothly. As a result, the reaction resistance of the entire air electrode is suppressed, the electrode activity is increased, and a high SOFC output is realized.

  In the technique disclosed herein, when the parameter P is 1.4 or less, the first particles and the second particles are joined to form a good interface with respect to the movement of oxygen ions. Judgment can be made. The parameter P is preferably 1.25 or less, more preferably 1.2 or less, and particularly preferably 1.15 or less.

As the specific surface area S of the composite particles, the specific surface area value measured for the composite particles contained in the electrode material disclosed herein can be used. Further, as the theoretical specific surface area S ′, for example, as shown in the following formula, the specific surface area value of the first particles and the specific surface area value of the second particles used for the production of the composite particles are determined according to the blending ratio. The sum (weighted sum) can be used.
Theoretical specific surface area S ′ = (specific surface area of the first particle × addition ratio) + (specific surface area of the second particle × addition ratio)

In this specification, the specific surface areas of the composite particles, the first particles, and the second particles are measured based on the BET method by measuring the amount of gas (typically nitrogen (N ₂ ) gas) physically adsorbed on the surfaces of the particles. It is possible to adopt a value calculated by dividing all the external and internal surface areas of the primary particles constituting the particles by their masses. Such a specific surface area can be measured in accordance with JIS Z 8830: 2013 (ISO 9277: 2010) “Method for measuring specific surface area of powder (solid) by gas adsorption”.

  The electrode resistance R is an electrode reaction resistance measured by an alternating current impedance method for an electrode having a thickness of 10 μm or more and 100 μm or less formed using composite particles or first particles. This electrode reaction resistance can be measured based on the method described in the following Example, for example. In addition, the electrode is prepared by mixing an electrode forming paste prepared by blending the composite particles or the first particles in an appropriate dispersion medium so that the solid content concentration is 70% by mass, and using an appropriate substrate (for example, cerium oxide). It can be formed by feeding it above, drying and baking. Here, as the dispersion medium, for example, a vehicle in which polyvinyl butyral (PVB) as a binder and xylene as a solvent are mixed at a ratio of 3:17 can be suitably used. In addition, the supply of such paste can preferably employ, for example, a screen printing method from the viewpoint that the electrodes can be accurately formed.

By using composite particles having the above-described configuration, the electrode material disclosed herein has higher oxygen ion conductivity and more resistance between the first oxide and the second oxide. It can be kept lower.
As described above, the first oxide (for example, the first particle) and the second oxide (for example, the second particle) are both mixed conductors (oxygen) having both oxygen ion conductivity and electron conductivity. Ion-electron mixed conductor). In addition, since the first oxide (for example, the first particles) and the second oxide (for example, the second particles) are joined by a mechanical method, a favorable interface is formed for the passage of oxygen ions. The contact resistance between the particles is suitably reduced. Therefore, the electrode material containing these composite particles is not only a so-called three-phase interface (interface where the air electrode (electron conductor) and electrolyte (ion conductor) are in contact with the gas phase), but also the electrode surface (surface of the electrode material). Can also be an excellent reaction field. For this reason, when an SOFC component (for example, an electrode (typically an air electrode) or a current collector) is manufactured using the electrode material disclosed herein, the solid oxide has a lower resistance and higher performance. A fuel cell can be realized. Preferably, for example, an electrode that can exhibit high electrode performance with low resistance even in a relatively low temperature range (for example, 600 ° C. to 700 ° C.) can be realized.

(SOFC)
More specifically, in another aspect, the solid oxide fuel cell (SOFC) provided by the technology disclosed herein essentially comprises a fuel electrode (anode), a solid electrolyte, and an air electrode (cathode). ) And are provided. Here, the SOFC is, for example, a conventionally known flat plate type (Planar), MOLB type, vertically striped cylindrical type (Tubular), a flat cylindrical type (Flat tubular) in which the peripheral side surface of the cylinder is vertically crushed, an integral laminated type, or the like. The SOFC may have various structures. Further, the shape and size of an electrode (typically an air electrode) using the electrode material disclosed herein are not particularly limited. The support (base material) that supports the SOFC is not particularly limited, and may be, for example, a fuel electrode (anode support type), an air electrode (cathode support type), a solid electrolyte (solid electrolyte support type), and the like.

  Therefore, the SOFC disclosed herein will be described in more detail with reference to FIG. FIG. 1 is a cross-sectional configuration diagram schematically illustrating a part of a power generation system including the SOFC 10 disclosed herein. This figure is drawn schematically, and the dimensional relationship (length, width, thickness, etc.) in the diagram does not reflect the actual dimensional relationship. The SOFC 10 having the structure shown here is an anode-supported SOFC, and is formed on a cylindrical fuel electrode (anode) 40 serving as a support and at least a part of the surface of the fuel electrode 40 (film-like). ) A solid electrolyte 30 and a thin plate-like or sheet-like air electrode (cathode) 20 formed on the surface of the solid electrolyte 30 are stacked. Although not shown in this example, a reaction preventing layer for preventing the reaction between the air electrode 20 and the solid electrolyte 30 may be provided.

An end 42 of the fuel electrode 40 and a joint surface of a gas pipe 60 that supplies fuel gas (typically hydrogen (H ₂ ) or hydrocarbon (for example, methane; CH ₄ )) are connected by the connecting member 50. It is joined and sealed so that gas (fuel gas or air) does not flow out or in. The air electrode 20 is typically exposed to the outside air so as to be exposed to a gas containing oxygen (O ₂ ). It is comprised so that it may become a structure.
When a current is applied to the SOFC 10, oxygen in the oxygen-containing gas (typically air) becomes oxygen ions (O ²⁻ ) in the air electrode 20. The oxygen ions are supplied from the air electrode 20 to the fuel electrode 40 through the solid electrolyte 30. Then, the fuel electrode 40 reacts with the fuel gas to generate water (H ₂ O) and emit electrons, thereby generating electric power.

  Here, the fuel electrode 40 constituting the SOFC 10 has a porous structure. The shape of the fuel electrode 40 only needs to be configured so as to be in contact with the fuel gas supplied to the SOFC 10, and can be appropriately selected according to the shape of the SOFC described above. Since the SOFC 10 having the configuration shown in FIG. 1 is a so-called anode support type, a thin plate-like or sheet-like fuel electrode 40 formed relatively thick is formed as a support for the SOFC 10. Although not shown, the fuel electrode 40 portion may be divided into an anode support portion and a fuel electrode (anode). The thickness (overall) of the fuel electrode 40 as the support is preferably set in consideration of handling properties, durability, coefficient of thermal expansion, and the like. Typically, it is about 0.1 mm to 10 mm, and preferably about 0.5 mm to 5 mm, but is not limited to this thickness.

  As a material constituting such a fuel electrode, one or two or more materials conventionally used for SOFC can be used without any particular limitation. For example, nickel (Ni), copper (Cu), gold (Au), platinum (Pt), palladium (Pd), ruthenium (Ru) and other platinum group elements, cobalt (Co), lanthanum (La), strontium (Sr ), A metal oxide composed of one or more of metals and / or metal elements composed of titanium (Ti) or the like. Specific examples include metals and metal oxides made of platinum group elements such as Ni, Co, and Ru. For example, Ni is a particularly preferable metal species because it is cheaper than other metals and has a sufficiently high reactivity with fuel gas such as hydrogen. Moreover, the composite which mixed these metals and metal oxides can also be used. Further, for example, a composite of the fuel electrode constituent material (metal or metal oxide) and a solid electrolyte constituent material described later can be used. Specifically, for example, nickel (Ni) or ruthenium (Ru) and stabilized zirconia (for example, yttria stabilized zirconia (YSZ), calcia stabilized zirconia (CSZ), scandia stabilized zirconia (ScSZ), etc.). Cermet is a preferred example. Although not particularly limited, for example, the mixing ratio (mass ratio) of the fuel electrode constituent material and the solid electrolyte constituent material described later is about 90:10 to 40:60 (more preferably about 80:20 to 45). : 55).

  The solid electrolyte 30 constituting the SOFC 10 disclosed herein has a dense structure. The solid electrolyte 30 is laminated on the fuel electrode 40, and the shape thereof can be appropriately changed according to the shape of the fuel electrode 40. Further, the thickness of the solid electrolyte 30 is increased so that the denseness of the solid electrolyte layer is maintained, while the thickness of the solid electrolyte 30 is balanced so that the thickness can be reduced to provide oxygen ion conductivity preferable as SOFC. Is preferably set. Typically, the thickness is about 0.1 μm to 50 μm, preferably about 1 μm to 40 μm, and more preferably about 5 μm to 20 μm. However, the thickness is not limited thereto.

As a material constituting such a solid electrolyte, one or more kinds of materials conventionally used in SOFC can be used without particular limitation, and for example, a compound having high oxygen ion conductivity is preferably used. It is done. For example, cerium (Ce), zirconium (Zr), magnesium (Mg), scandium (Sc), titanium (Ti), aluminum (Al), yttrium (Y), calcium (Ca), gadolinium (Gd), samarium (Sm) ), Barium (Ba), lanthanum (La), strontium (Sr), gallium (Ga), bismuth (Bi), niobium (Nb), tungsten (W), etc. Preferably there is. Specifically, stabilizers (for example, yttria (Y ₂ O ₃ ), calcia (CaO), scandia (Sc ₂ O ₃ ), magnesia (MgO), ytterbia (Yb ₂ O ₃ ), erbia (Er ₂ O ₃ )) whose crystal structure has been stabilized, zirconia (ZrO ₂ ), dopants (eg gadolinia (Gd ₂ O ₃ ), lanthania (La ₂ O ₃ ), samaria (Sm ₂ O ₃ ), yttria (Y _A suitable example is cerium oxide (CeO ₂ ) doped with ₂ O ₃ )). For example, yttria-stabilized zirconia (YSZ) doped with an oxide of yttrium (Y) (eg, yttria (Y ₂ O ₃ )) or scandium (Sc) oxide (eg, scandia (Sc ₂ O ₃ )) is used. Doped scandia-stabilized zirconia (ScSZ) or the like can be preferably used.

The air electrode (cathode) 20 constituting the SOFC disclosed here has a porous structure like the fuel electrode 40. The air electrode 20 is laminated on the solid electrolyte 30, and the shape thereof can be appropriately changed according to the shape of the solid electrolyte 30. The thickness of the air electrode 20 is typically about 1 μm to 200 μm, preferably about 5 μm to 100 μm, more preferably 10 μm to 100 μm, but is not limited to such thickness.
The air electrode 20 can be suitably manufactured by any of the electrode materials disclosed herein. Since the air electrode composed of this electrode material has improved oxygen ion conductivity and electronic conductivity, SOFCs equipped with such an air electrode have high power generation performance (even in a relatively low operating temperature range). For example, a power density of 0.54 W / cm ² or more can be exhibited under conditions of an operating temperature of 700 ° C. and a current of 0.5 A / cm ² . The power density measurement conditions will be described in detail in the examples described later.

  Although not particularly shown, in a cell stack in which a plurality of SOFCs (single cells) 10 are connected, adjacent cells are connected by a current collector. Since this current collector also has a role as a partition wall that partitions the SOFC fuel electrode 40 and the air electrode 20, in addition to high electrical conductivity, it is suitable for both oxidizing atmospheres and reducing atmospheres at high temperatures. It is required to have resistance. The electrode material disclosed here can also be preferably used as the material for the current collector of the SOFC 10. Furthermore, it can be preferably used as a bonding material (bonding paste) for airtightly bonding the current collector and the air electrode. In addition, the current collector referred to in the present specification includes structural members called interconnectors, separators, etc. in SOFC, for example, joining the air electrode of one cell and the fuel electrode of the other cell, It may be a member that connects one air electrode and another component.

The above electrode materials can be produced by forming the above electrode materials as they are alone or together with additives such as sintering aids and pore formers into desired forms and firing them, thereby producing components such as target electrodes. can do.
In such molding, for example, the powdered electrode material may be molded as it is, or prepared in the form of a paste (including ink, slurry, etc.) in which the powdered electrode material is dispersed in a dispersion medium. May be used. Any dispersion medium may be used as long as it can disperse the electrode material disclosed herein well, and various dispersion media used in this type of conventional paste can be used without particular limitation. Typically, as such a dispersion medium, a mixture of a vehicle and an organic solvent for viscosity adjustment can be considered. As such an organic solvent, for example, one kind of high-boiling organic solvents such as ethylene glycol and diethylene glycol derivatives (glycol ether solvents), toluene, xylene, butyl carbitol (BC), terpineol, or two or more kinds are used. Can be used in combination. 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 dispersion medium may contain any additive that can be generally used for this type of dispersion medium, such as a dispersant and a plasticizer.

  The ratio of the dispersion medium can be adjusted as appropriate according to the specification purpose of the electrode material. For example, it can be appropriately adjusted according to the form of the SOFC electrode and other components, the method employed for the molding, and the like. For example, such a paste-like electrode material can be preferably used to form the above-mentioned SOFC constituent member by printing or the like. More specifically, for example, when a green sheet for producing an SOFC air electrode is formed by a method such as screen printing or a doctor blade method, the dispersion medium is used for the entire paste (that is, for example, The ratio of the electrode material, the pore former, and the dispersion medium) is about 5% by mass to 60% by mass, preferably 7% by mass to 50% by mass, and more preferably 10%. It is not less than 40% by mass. 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 electrode material can be easily formed (applied) as a layered body (for example, a coating film) with a uniform thickness, is easy to handle, and further removes the solvent from the molded body. It is suitable because it does not take a long time to do. 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 electrode material and the dispersion medium. By adjusting the viscosity of the paste-like electrode material to an appropriate viscosity according to the desired application, the electrode material can be easily supplied to the desired position in the desired form in the form of coating or printing. . 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. In addition, when forming the SOFC air electrode with the electrode material disclosed herein, the entire air electrode may be composed of the electrode material, or only part of the air electrode may be composed of the air material. good. The electrode material disclosed herein can be used as 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 electrode material prepared as described above can be fired in the same manner as this conventional component member. 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 constituent member such as an SOFC air electrode or a current collector can be produced.

  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 electrode material]
As the first oxide (first particle), a perovskite oxide (average particle diameter 2 μm) having a basic composition of La _0.6 Sr _0.4 (Co _0.2 Fe _0.8 ) O _3-δ is used. In addition, La ₂ NiO ₄ (average particle diameter 0.2 μm) was prepared as the second oxide (second particle).
These oxides were weighed according to the formulations shown in Examples 1 to 8 in Table 1 below, and mixed (not depending on the mechanical technique) to produce electrode materials composed of the particles of Examples 1 to 8. In addition, these oxides were weighed in the formulations shown in Examples 9 to 15 in Table 1 below, and composited by a mechanical method to produce electrode materials composed of the composite particles of Examples 9 to 15. For compounding by a mechanical method, a dry particle compounding device (Nosoluta manufactured by Hosokawa Micron Co., Ltd.) capable of compounding and coating fine particles by a dry method is used, and the power is 3.0 and the operation time is 10 minutes. The compounding process was performed under the following conditions.

[Production of SOFC cell for evaluation]
The electrode materials of Examples 1 to 15 prepared above were used as SOFC air electrode materials, and SOFC cells for evaluation were produced by the following procedure.
That is, first, nickel oxide (NiO, average particle size 0.5 μm) powder and 8% yttria-stabilized zirconia (8% YSZ, average particle size 0.5 μm) powder are mixed at a mass ratio of 60:40. Thus, a fuel electrode support material was prepared. Then, this fuel electrode support material, a pore former (carbon component), a binder (polyvinyl butyral; PVB), a plasticizer and a solvent (xylene) in this order 58: 5: 8.5: 4.5: By kneading at a mass ratio of 24, a paste-like composition for forming a fuel electrode support was prepared. Subsequently, this composition for forming a fuel electrode support was applied onto a carrier sheet in a sheet form by a doctor blade method and dried to form a fuel electrode support green sheet having a thickness of 0.5 to 1 mm.

  Next, the same nickel oxide powder, 8% YSZ powder, solvent (α-terpineol; TE) and binder (ethyl cellulose; EC) as above are mixed in a mass ratio of 48: 32: 18: 2. Thus, a fuel electrode forming composition was prepared. Next, this fuel electrode forming composition was supplied onto the fuel electrode support green sheet by screen printing and dried to form a fuel electrode green sheet having a thickness of about 10 μm.

  A composition for forming a solid electrolyte layer in the form of a paste by kneading the same 8% YSZ powder, binder (EC), and solvent (TE) as the solid electrolyte material at a mass ratio of 65: 4: 31. A product was prepared. A solid electrolyte layer green sheet having a thickness of about 10 μm was formed by supplying the sheet on the fuel electrode green sheet by a screen printing method.

Further, as a reaction preventing layer material, 10% gadolinium-doped ceria (10GDC) powder having an average particle diameter of 0.5 μm, a binder (EC), and a solvent (TE) are kneaded at a mass ratio of 65: 4: 31. As a result, a paste-like composition for the reaction preventing layer was prepared. This was supplied on the solid electrolyte layer green sheet in a sheet form by a screen printing method to form a reaction preventing layer green sheet having a thickness of about 5 μm.
The laminated green sheet thus prepared was cofired at 1350 ° C. to obtain a SOFC half cell. In addition, the shape of the half cell was a disk shape having a diameter of 20 mm.

Next, a composition for forming an air electrode was prepared using the electrode materials of Examples 1 to 15 prepared above as the air electrode material. That is, each electrode material, binder (EC), and solvent (TE) were kneaded at a mass ratio of 80: 3: 17 to obtain a paste-like composition for forming an air electrode. The air electrode layer green sheet was formed by supplying this into a circular sheet by the screen printing method on the SOFC half cell prepared above. Next, this was fired at 1100 ° C. to fire the air electrode, and SOFCs for evaluation of Examples 1 to 14 were obtained. The dimensions of the air electrode were 10 mm in diameter and about 30 μm in thickness.
The electrode resistance and power generation performance of the evaluation SOFC thus obtained were measured according to the following procedure.

[Electrode reaction resistance]
For the SOFCs of Examples 1 to 14, AC impedance measurement was performed in an open circuit state, and the electrode reaction resistance was calculated from the voltage loss during power generation. For the measurement of the AC impedance, a frequency response analyzer (manufactured by Solartron, model 1260) was used. Fuel electrode supply gas: hydrogen gas (50 ml / min), air electrode supply gas: air (100 ml / min), measurement temperature 700 ° C. In an open circuit state, measurement was performed under conditions of a measurement frequency region of 10 MHz to 0.1 Hz. The electrode reaction resistance was defined as the full width of a plurality of arc-shaped resistance components in the Cole-Cole plot obtained by AC impedance measurement. The measurement results of the electrode reaction resistance are shown in the column “R” in Table 1.

[Power generation performance]
The power density when the SOFCs of Examples 1 to 14 were operated under the following conditions was measured, and the maximum power density (W / cm ² ) was shown as the power generation performance in the “Power generation performance” column of Table 1.
Fuel electrode supply gas: Hydrogen gas (50 ml / min)
Air electrode supply gas: Air (100 ml / min)
Operating temperature: 700 ° C

  Further, specific surface areas of the prepared powders of the first particles and the second particles and the electrode materials of Examples 1 to 15 were measured based on the BET method using nitrogen gas. Then, the parameter P was calculated from the result and the measurement result of the reaction resistance based on the formula: P = R × S × (S / S ′). The results are shown in the column “S” of Table 1 for the specific surface area of the electrode material of Examples 1 to 15, and in the column of “S ′” for the theoretical specific surface area of the electrode material of Examples 1 to 15 for the parameter P. Is shown in the column “P”. In addition, the specific surface area S of the electrode material of Examples 1-8 is a specific surface area of the 1st particle | grains and 2nd particle | grains mixed by the predetermined | prescribed ratio, and makes each specific surface area of a 1st particle | grain and a 2nd particle into a mixture ratio. Corresponds to the value added up accordingly.

[Evaluation]
As can be seen from the results of Examples 1 to 8, it can be seen that LSCF (first oxide) can constitute an air electrode that achieves good power generation performance when used alone. However, when mechanical treatment is not performed and mixed particles obtained by mixing LSCF (first oxide) and La ₂ NiO ₄ (second oxide) are used as the electrode material, the mixing ratio of La ₂ NiO ₄ It has been confirmed that the power generation performance decreases as the value increases.
In addition, since there is no significant change in power generation performance in comparison with Example 9 and Example 1, there is no significant impact on power generation performance whether or not LSCF single electrode material is subjected to mechanical treatment. It could be confirmed. That is, it can be seen that the effect of adjusting the interface state by mechanical processing is difficult to obtain by mere composite integration of a single material having the same crystal structure.

Then, as shown in Examples 10 to 15, each material of Examples 1 and 8 is obtained by compounding LSCF (first oxide) and La ₂ NiO ₄ (second oxide) by mechanical processing. It was found that the power generation performance was improved as compared with the case of the single case. That is, the first particles and the second particles having different crystal structures are integrally joined to each other, in addition to the properties (for example, oxygen ion conductivity and auxiliary properties) of each material itself, mechanical processing It has been confirmed that the effect of adjusting the interface state due to the above has been demonstrated and contributed to the improvement of power generation performance. The proportion of La ₂ NiO _{4 in} the composite particles is preferably from 0.1 to 20% by mass, more preferably from 1 to 10% by mass, and even more preferably in the vicinity of 5% by mass. I understood.

From the above, it was confirmed that an SOFC excellent in power generation performance can be realized, for example, by forming a low temperature operation type SOFC air electrode using the electrode material disclosed herein. Such an electrode material is suitable for forming an SOFC air electrode, for example, a current collector disposed between the air electrode and the interconnector, or an interconnector itself. Also, it can be preferably used.
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.

10 Solid oxide fuel cell (SOFC)
20 Air electrode (cathode)
30 Solid electrolyte 40 Fuel electrode (anode)
50 connecting member 60 gas pipe

Claims (7)

An electrode material used to form an electrode of a solid oxide fuel cell,
Having a perovskite crystal structure, the general _{formula: (Ln 1-x Sr x} ) BO 3-δ;
(Here, Ln represents at least one lanthanoid element, B represents at least one element selected from Ni, Co, Mn, Cr, Cu, Fe and Ti, and 0.1 ≦ x ≦ 0. 9 and δ is a value determined to satisfy the charge neutrality condition),
General formula: X ₂ NiO _{4-δ ′} (where X includes at least one element selected from La, Pr and Nd, and δ ′ is a value determined to satisfy the charge neutrality condition); A second oxide represented by:
An electrode material comprising composite particles in which the second oxide is bonded to the surface of the first oxide by a mechanical method. The composite particles are:
The electrode material according to claim 1, wherein the electrode material is formed by dry-mixing the first particles containing the first oxide and the second particles containing the second oxide by a mechanical method. An actual measurement S of the specific surface area of the composite particles;
A theoretical specific surface area S ′ defined as the sum of the specific surface areas of the first and second particles used to form the composite particles;
For an electrode having a thickness of 10 μm or more and 100 μm or less formed using the composite particles, an electrode resistance R measured by an AC impedance method;
Based on the following formula: P = R × S × (S / S ′);
The electrode material according to claim 2, wherein the parameter P defined by: satisfies P ≦ 1.4.   The ratio of the said 2nd oxide which occupies for the sum total of a said 1st oxide and a said 2nd oxide exceeds 0 mass%, and is 50 mass% or less, The any one of Claims 1-3 The electrode material according to item.   The structural member of the solid oxide fuel cell comprised from the electrode material of any one of Claims 1-4.   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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