JP2005050636A - Contact material for air electrode and solid oxide fuel cell (sofc) using this - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a contact material for an air electrode excellent in power generating performance under an air environment and capable of restraining destruction of unit cells without damaging an intrinsic power generating performance of the unit cells, as well as a solid oxide fuel cell using the material, in case of use for an air electrode contact layer of the solid oxide fuel cell. <P>SOLUTION: The contact material for the air electrode contains at least silver powder or silver alloy powder and perovskite oxide powder. As the perovskite oxide, lanthanam-cobalt system oxide is preferred. Further, the solid oxide fuel cell made by laminating unit cells in multiple layers through separators each jointing fuel electrode on one face of a solid electrolyte showing oxygen ion conductivity and jointing the air electrode on the other face has the air electrode contact layer intercalated between the air electrode and the separator. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a contact material for an air electrode of a solid oxide fuel cell and a solid oxide fuel cell using the contact material for an air electrode.

  A solid oxide fuel cell (hereinafter referred to as “SOFC”) is a fuel cell using a solid electrolyte exhibiting oxygen ion conductivity as an electrolyte. Since this SOFC is a solid electrolyte, there is no problem of electrolyte dissipation and a long life can be expected. Moreover, since the operating temperature is as high as about 600 to 1000 ° C., the utility value of waste heat is also high. Furthermore, since the output density is high, compactness and high efficiency can be expected.

  In general, SOFC battery structures are roughly classified into a flat plate type, a cylindrical type, and an integral type. Of these, the flat SOFC has an anode electrode in which a fuel electrode such as hydrogen or city gas is in contact with one surface of a flat solid electrolyte and an oxidant gas such as air or oxygen is in contact with the other surface. It has a laminated structure in which a single cell joined with a plurality of layers is laminated via a separator. Since this flat SOFC has a relatively low internal resistance, it has the advantages of high power generation efficiency and high output density per unit volume for stacking thin single cells.

  When fuel gas and oxidant gas are supplied to the fuel electrode and air electrode of such a flat plate type SOFC, there is a difference between the oxygen partial pressure on the air electrode side and the oxygen partial pressure on the fuel electrode side. Therefore, oxygen becomes ions in the air electrode and is transported to the fuel electrode through the solid electrolyte, and the oxygen ions that have reached the fuel electrode react with the fuel gas and emit electrons. Therefore, if a load is connected to the fuel electrode and the air electrode, the change in the free energy of the cell reaction can be directly taken out as electric energy to generate electric power.

  By the way, when the single cells are stacked in multiple stages via separators, it is important for the design of the flat plate type SOFC to reduce the contact resistance between the two electrodes (air electrode, fuel electrode) and the separator. This is because, even if the power generation performance inherent in a single cell is excellent, if the contact resistance between the electrode (air electrode, fuel electrode) and the separator is large, the current collection efficiency decreases, and the power generation performance of the flat plate SOFC as a whole This is because of damage.

  Therefore, conventionally, for example, by interposing an air electrode contact layer between the air electrode and the separator, the gap formed between the air electrode and the separator is filled to improve the adhesion between them, and the contact resistance is reduced. Thus, a technique for improving the current collection efficiency is known.

As a material for such an air electrode contact layer, for example, a perovskite type oxide (having a crystal structure of ABO ₃ ) such as lanthanum strontium cobaltite powder is dissolved in a binder and made into a paste (hereinafter referred to as “ABO ₃ ” Known as "system contact material"). Further, for example, a paste prepared by melting silver powder with a binder (hereinafter referred to as “silver-based contact material”) is known (see Patent Document 1).

  Furthermore, for example, silver powder and an oxide such as tin oxide, indium oxide, lanthanum oxide, etc., dissolved in a binder and pasted (hereinafter referred to as “silver-oxide contact material”) are known. According to the silver-oxide-based contact material, it is said that an air electrode contact layer having excellent mechanical strength can be obtained (see Patent Document 2).

JP-A-60-115164 JP 2002-216807 A

However, when the air electrode contact layer is formed using the conventional ABO ₃ type contact material, the electric resistance of the perovskite oxide itself is relatively high, so that the electricity generated by the single cell can be collected efficiently. However, there is a problem that the power generation performance of the flat plate SOFC is significantly lower than the power generation performance of the single cell.

In addition, when an air electrode contact layer is formed using a conventional silver-based contact material, power generation performance is improved when oxygen is supplied to the air electrode of the flat plate type SOFC, but when air is supplied. The power generation performance was only slightly improved as compared with the case where the air electrode contact layer was formed using the ABO ₃ system contact material. This is due to the fact that a dense silver film is formed on the surface of the air electrode by heating, so that in a high oxygen environment, oxygen can permeate sufficiently to the air electrode, but in a low oxygen environment. This is probably because oxygen was not sufficiently transmitted to the air electrode by the film.

  In addition, the single cell and the separator are fixed by silver, and the single cell breaks due to the difference in thermal expansion between the two. This is because the silver softened at the power generation temperature bites into the groove of the separator and enters the pores of the porous air electrode to some extent. It is considered that the single cell was cracked due to the difference in thermal expansion between the two.

  Moreover, in the air electrode contact layer formed using the conventional silver-oxide type paste, the electric conductivity of the air electrode contact layer is low, and the power generation performance is not sufficient.

  Therefore, the problem to be solved by the present invention is that when used in an air electrode contact layer of a solid oxide fuel cell, the power generation performance in an air environment is not significantly impaired without significantly degrading the power generation performance inherent in the single cell. An object of the present invention is to provide a contact material for an air electrode which is excellent and can suppress the destruction of a single cell. Another object of the present invention is to provide a solid oxide fuel cell using this contact material.

  In order to solve the above-mentioned problems, the air electrode contact material according to the present invention includes, as described in claim 1, at least silver powder or silver alloy powder and perovskite oxide powder. And

  In addition, as described in claim 2, the air electrode contact material further includes palladium (Pd), ruthenium (Ru), platinum (Pt), rhodium (Rh), iridium (Ir), and gold (Au). It includes a powder of one or more kinds of noble metals selected from the above or a powder of an alloy of the noble metals.

  Further, as described in claim 3, the gist of the air electrode contact material further includes a solvent.

  In addition, as described in claim 4, the gist of the air electrode contact material further includes a resin.

  In addition, as described in claim 5, the perovskite oxide is preferably a lanthanum-cobalt oxide.

  On the other hand, in the solid oxide fuel cell according to the present invention, the fuel electrode is joined to one surface of the solid electrolyte exhibiting oxygen ion conductivity, and the air electrode is joined to the other surface. In a solid oxide fuel cell in which a plurality of single cells are stacked through separators, an air electrode contact layer formed of the air electrode contact material is interposed between the air electrode and the separator. The gist of this is

  When the contact material for an air electrode according to the present invention is used as a material for an air electrode contact layer of a solid oxide fuel cell, the air electrode contact layer is compared with (1) a perovskite oxide simple substance. Due to low electrical resistance, (2) contribution to oxygen ion activation because it contains not only silver (silver alloy) but also perovskite oxide, and (3) porosity. Even when air is supplied to the air electrode, the power generation performance of the solid oxide fuel cell as a whole can be greatly improved without impairing the power generation performance of the single cell.

  Further, since the perovskite oxide in silver (silver alloy) contacts the separator not at the surface but at a point and acts as a so-called roller, slip occurs during cooling. Therefore, it is possible to effectively prevent the single cell from cracking due to the difference in thermal expansion.

  At this time, the air electrode contact material according to the present invention is further selected from palladium (Pd), ruthenium (Ru), platinum (Pt), rhodium (Rh), iridium (Ir) and gold (Au). When one or more kinds of noble metal powders or alloy powders of the noble metals are included, the heat resistance of the base silver (silver alloy) is improved. Can be suppressed.

  When the air electrode contact material further contains a solvent, various powders contained in the air electrode contact material can be uniformly dispersed and mixed to form a paste.

  Further, when the air electrode contact material further contains a resin, the paste state of the air electrode contact material can be stably maintained, and a uniform film can be applied when applied to the air electrode and / or the separator. There exists an advantage which becomes easy to form.

  The perovskite oxide in the air electrode contact material is preferably a lanthanum-cobalt oxide. This is because it is excellent in electronic conductivity and oxygen ion conductivity, and is advantageous in improving power generation performance.

  The solid oxide fuel cell according to the present invention having an air electrode contact layer formed from the air electrode contact material is excellent in power generation performance not only in an oxygen environment but also in an air environment. In addition, since the internal single cell is not easily destroyed, it has high reliability.

  Hereinafter, the contact material for an air electrode according to the present invention (hereinafter also referred to as “the present contact material”) and a solid oxide fuel cell using the present contact material (hereinafter referred to as “the present SOFC”) may be used. ) Will be described in detail.

  First, the configuration of the contact material will be described. This contact material is used to form an air electrode contact layer of a solid oxide fuel cell, and contains at least silver powder or silver alloy powder and perovskite oxide powder.

  In the present contact material, the silver powder refers to pure silver powder. The silver alloy powder refers to a metal powder containing silver as a main component and mixed with silver and one or more other elements. Other elements in the silver alloy powder include palladium (Pd), ruthenium (Ru), platinum (Pt), rhodium (Rh), iridium (Ir), gold (Au), copper (Cu), and zinc (Zn). , Nickel (Ni), cadmium (Cd), tin (Sn), and the like. Among these, since it is excellent in the heat resistance of a silver alloy, the stability of a high temperature state, etc., palladium (Pd) can be used suitably as another element. Note that both the silver powder and the silver alloy powder may contain impurities that cannot be removed.

In this contact material, the perovskite oxide powder refers to an oxide powder having a perovskite crystal structure of the general formula ABO ₃ , and the A metal and B metal can be replaced with other metals. Among them, the oxide LaMO ₃ in which the A metal is La and the B metal is the transition metal M (M = Co, Mn, Fe) can be preferably used from the viewpoint of high conductivity. Among these, (La, AE) MO ₃ (AE = Sr, Ca; M = Co, Mn, Fe) in which a part of La is replaced with an alkaline earth metal AE (AE = Sr, Ca) is conductive. From the point that various properties such as the thermal expansion coefficient can be adjusted, it can be used more suitably. Most preferably, La _1-x Sr _x CoO ₃ (x = 0.1 to 0.5) can be used from the viewpoint of excellent balance between catalytic activity, conductivity, and stability.

  In this contact material, the mixing ratio of the silver powder or silver alloy powder to the perovskite oxide powder is as follows: silver powder or silver alloy powder: perovskite oxide powder = 90: 10% by weight to 30% : The range of 70 weight% is preferable. More preferably, silver powder or silver alloy powder: perovskite oxide powder = 70: 30 wt% to 50:50 wt%.

  The reason why the range of the mixing ratio is preferable is that when the content of silver powder or silver alloy powder is low and the content of perovskite oxide powder is high, the electrical resistance of the air electrode contact layer obtained is When the content of silver powder or silver alloy powder is high and the content of perovskite oxide powder is low, the air electrode tends to decrease. This is because the porous property of the contact layer is lost, the performance in an air atmosphere is lowered, and the single cell tends to be easily broken by fixing.

  This contact material contains the above-mentioned silver powder or silver alloy powder and perovskite oxide powder as essential constituent elements, but may further contain the following as optional constituent elements. .

  That is, in this contact material, palladium (Pd), ruthenium (Ru) is used from the viewpoint of improving the heat resistance of the air electrode contact layer formed from this contact material and suppressing the consumption of the air electrode contact layer. , Platinum (Pt), rhodium (Rh), iridium (Ir), and gold (Au) may be one or more kinds of noble metal powders or powders of the noble metal alloys. . Among these, palladium (Pd) powder can be suitably used from the viewpoint of improving the stability of silver (Ag) in the vicinity of the operating temperature of the solid oxide fuel cell.

  The noble metal powder or the noble metal alloy powder is preferably mixed in an amount of 1 to 15% by weight with respect to the silver powder or the silver alloy powder. More preferably, it is in the range of 1 to 5% by weight.

  In this case, the mixing ratio of the mixed powder of the silver powder or the silver alloy powder and the noble metal powder or the noble metal alloy powder and the perovskite oxide powder is a mixed powder: perovskite oxide powder. The range of body = 90: 10 wt% to 30:70 wt% is preferable. More preferably, the mixed powder: perovskite type oxide powder = 70: 30 wt% to 50:50 wt%.

  Further, the contact material may contain a solvent in order to disperse and mix various powders contained in the contact material into a paste. This solvent is volatilized by drying after the application of the contact material, or decomposes and disappears when the SOFC is heated for the first time.

  As the solvent, either an organic solvent or an inorganic solvent can be used, and it is not particularly limited as long as the above various powders can be uniformly dispersed and mixed. Preferably, an organic solvent is preferably used because it is excellent in coating property when the contact material is applied.

  In the case of using an organic solvent as the solvent, specifically, n-paraffin, turpentine oil, diethylene glycol, diethylene glycol monobutyl ether acetate, polyethylene glycol and the like may be mentioned, and these may be used alone or in combination of two or more.

  On the other hand, when an inorganic solvent is used as the solvent, specific examples include water.

  The blending amount of the solvent can be appropriately adjusted in consideration of the dispersion / mixing state of various powders, the viscosity of the obtained paste, and the like.

  In addition, the contact material contains one or more resins such as cellulose resin, polyvinyl alcohol resin, acrylic resin, and terpene resin from the viewpoint of stably maintaining the paste state of the contact material. May be. This resin decomposes and disappears when the SOFC is heated for the first time.

  In addition, other plasticizers such as dimethyl phthalate, dibutyl phthalate, butyl benzyl phthalate, fatty acid salts, benzene sulfonates, polyhydric alcohols, fatty acid glycerol are also included in the contact material as necessary. One or two or more various additives such as dispersants such as esters may be contained, and are not particularly limited.

  Next, the manufacturing method of this contact material is demonstrated. The method for producing the contact material is not particularly limited as long as each powder can be uniformly dispersed and mixed. For example, a predetermined amount of the above-mentioned silver powder, silver alloy powder, or noble metal powder is weighed and placed in a kneading apparatus such as a strong kneader together with a solvent, a resin, and various additives as necessary, for 1 to 2 hours. After kneading to a certain degree, a method of adding a predetermined amount of perovskite oxide powder and kneading for about 1 to 2 hours may be mentioned.

  Next, the present SOFC using the present contact material will be described.

  This SOFC is a solid oxide fuel comprising a single cell in which a fuel electrode is joined to one surface of a solid electrolyte exhibiting oxygen ion conductivity, and a single cell having an air electrode joined to the other surface via a separator. In the battery, an air electrode contact layer formed of the present contact material is interposed between the air electrode and the separator.

  The battery structure of this SOFC is preferably a flat plate type. At this time, the flat plate type is roughly classified into two types: a self-supporting membrane type in which a solid electrolyte is self-supporting, and a supporting membrane type in which an electrode also has a supporting function, but this SOFC may be of any type. There is no particular limitation.

The solid electrolyte is not particularly limited as long as it exhibits oxygen ion conductivity. Specifically, as the solid electrolyte, scandia-stabilized zirconia (hereinafter referred to as “ScSZ”) to which ₃ to 6 mol% of scandia (Sc ₂ O ₃ ) is added as a stabilizer, 9 to 12 mol% of scandia ( ScSZ added with Sc ₂ O ₃ ), yttria stabilized zirconia added with 8 to 10 mol% of yttria (Y ₂ O ₃ ) (hereinafter referred to as “YSZ”), zirconia stabilized with other oxides, Examples include ceria (CeO ₂ ) -based solid electrolytes. These may be composites with ₂ % by weight or less of alumina (Al ₂ O ₃ ).

  For the fuel electrode, a material that is chemically stable under a high-temperature reducing atmosphere and has high electronic conductivity is used. Specific examples of such a material include Ni / YSZ cermet, Ni / ScSZ cermet, and the like, which are cermets of a catalyst and a solid electrolyte exhibiting oxygen ion conductivity. The material may be used and is not particularly limited.

For the air electrode, a material that is chemically stable under a high-temperature oxidizing atmosphere and has high electronic conductivity is used. Specific examples of such materials include noble metals such as platinum, and composite oxides such as LaSrMnO ₃ , LaCaMnO ₃ , LaMgMnO ₃ , LaSrCoO ₃ , LaCaCoO _3, etc. The material may be used and is not particularly limited. The air electrode may include only the above-described material, or may be a composite of the above-described material and a solid electrolyte exhibiting oxygen ion conductivity such as YSZ.

For the separator, a material that is an electronic conductor and is so small that ion conductivity is negligible and thermodynamically stable at a high temperature is used. Specific examples of such a material include lanthanum-chromium oxides such as LaCrO ₃ , stainless steel, Ni—Cr alloy, and the like. In the present invention, any material is used. There is no particular limitation.

  Next, a method for manufacturing the present SOFC will be described. First, a solid electrolyte material exhibiting oxygen ion conductivity is formed into a predetermined shape and sintered at a predetermined temperature. At this time, as a method for forming the solid electrolyte material, for example, a press forming method, a tape forming method, or the like may be used. In addition, as the sintering conditions for the solid electrolyte, an optimum temperature is selected according to the composition.

  Next, a slurry containing a fuel electrode material is applied to one surface of the solid electrolyte and sintered to form a fuel electrode. Similarly, a slurry containing an air electrode material is applied to the other surface of the solid electrolyte and sintered to form an air electrode. Further, the contact material is applied to the air electrode and / or the separator on the air electrode side of the obtained single cell. In this case, the contact material is preferably applied to a thickness of about 25 μm from the viewpoint of eliminating non-contact portions caused by variations in cell thickness and separator collector height, but is particularly limited. is not.

  In the above, specific examples of the method for applying the contact material include a spray method, a brush coating method, and a screen printing method. Specific examples of the method for applying the fuel electrode material and the air electrode material include a screen printing method, a doctor blade method, a brush coating method, a spray method, and a dipping method. However, in the present invention, both methods may be used for both coating methods and are not particularly limited.

  The SOFC can be obtained by stacking a fuel electrode, a solid electrolyte, an air electrode, a contact material, and a separator as a repetitive unit. When the present SOFC is started for the first time, a porous air electrode contact layer is formed from the contact material applied to the air electrode and / or the separator by heating at the time of raising the temperature. The air electrode contact layer is interposed therebetween.

  Hereinafter, the present contact material and the present SOFC will be described more specifically with reference to examples.

(Preparation of this contact material and comparative contact material)
(Example 1)
First, the present contact material was prepared by the following procedure. That is, a predetermined amount of each powder was weighed so that a mixing ratio of Ag powder: Pd powder = 98: 2 wt% was obtained. Then, mixed powder of Ag powder and Pd powder: La _0.6 Sr _0.4 CoO ₃ (hereinafter referred to as “LS _0.4 C”) powder = 20: 80 wt% A predetermined amount of the powder was weighed.

Next, after adding diethylene glycol monobutyl ether acetate, n-paraffin, turpentine oil and cellulose resin to a predetermined amount of the above mixed powder and kneading for 2 hours, LS _0.4 C powder and 2-propanol were further added to add 2 The contact material according to Example 1 in a paste state was obtained by kneading for a time.

(Example 2)
A contact material according to Example 2 was obtained in the same manner as in Example 1 except that the mixing ratio of Ag powder and Pd powder: LS _0.4 C powder = 40: 60 wt% was used.

(Example 3)
A contact material according to Example 3 was obtained in the same manner as in Example 1, except that the mixing ratio of Ag powder and Pd powder: LS _0.4 C powder = 50: 50 wt% was used.

(Example 4)
In Example 1, instead of LS _0.4 C powder, Sm _0.6 Sr _0.4 CoO ₃ (hereinafter referred to as “SmS _0.4 C”) powder was used, and Ag powder and Pd powder were used. A contact material according to Example 4 was obtained in the same manner except that the mixing ratio was: SmS _0.4 C powder = 50: 50 wt%.

(Example 5)
A contact material according to Example 5 was obtained in the same manner as in Example 1, except that the mixing ratio of Ag powder and Pd powder: LS _0.4 C powder = 70: 30 wt%.

(Comparative Example 1)
LS _0.4 C powder was melted with polyethylene glycol to make a paste, and an ABO ₃ -based contact material according to Comparative Example 1 was obtained.

(Comparative Example 2)
In Example 1, SnO ₂ powder which is an oxide powder other than the perovskite oxide powder was used instead of the LS _0.4 C powder, and a mixed powder of Ag powder and Pd powder: SnO ₂ powder = 62 A silver-oxide-based contact material according to Comparative Example 2 was obtained in the same manner except that the mixing ratio was 8: 37.2 wt% (corresponding to SnO ₂ powder: 47 vol.%).

(Comparative Example 3)
La _0.8 Sr _0.2 CoO ₃ (hereinafter referred to as “LS _0.2 C”) powder was melted with polyethylene glycol to form a paste, and an ABO ₃ -based contact material according to Comparative Example 3 was obtained.

(Comparative Example 4)
In Example 1, a silver-based contact material according to Comparative Example 4 was obtained in the same manner except that LS _0.4 C powder and 2-propanol were not used.

(Comparative Example 5)
In Example 1, Ag powder: Pd powder = 95: 5% by weight, and the silver according to Comparative Example 5 was similarly used except that LS _0.4 C powder and 2-propanol were not used. A system contact material was obtained.

In the above, Ag powder is manufactured by Shoei Chemical Industry Co., Ltd. (trade name “Ag-128”, 50% diameter: 2.2 μm), and Pd powder is manufactured by Shoei Chemical Industry Co., Ltd. (trade name “Pd”). -215 ”, 50% diameter: 0.7 μm), LS _0.4 C powder is manufactured by Seimi Chemical Co., Ltd. (50% diameter: 1.1 μm), SmS _0.4 C powder is Seimi Chemical Co., Ltd. Manufactured (50% diameter: 1.6 μm), SnO ₂ powder is manufactured by Kishida Chemical Co., Ltd. (50% diameter: 1.3 μm), and LS _0.2 C powder is manufactured by Seimi Chemical Co., Ltd. (50% diameter). : 2.4 μm).

  Here, the 50% diameter means a value of 50% diameter in a volume-based integrated fraction measured in accordance with JIS R1629. JIS R1629 is a standard for particle size distribution measurement method of fine ceramic raw material by laser diffraction / scattering method. Specifically, it is detected by irradiating fine ceramic raw material particles dispersed in liquid phase with laser light. This defines the method for measuring the particle size distribution using the scattered intensity distribution. At this time, in measuring the 50% diameter of each powder, the sample collection method and sample preparation method were performed in accordance with JIS M8100 and JIS R1622, respectively.

  As a particle size distribution measuring device by the laser diffraction / scattering method, for example, “Laser diffraction / scattering type particle size distribution measuring device” manufactured by HORIBA, Ltd. can be used. If it is, it will not specifically limit.

  As the particle size distribution of each powder to be used, the distribution of the abundance ratio on a volume basis is preferably as sharp as possible (individual particle diameters are uniform) and broad (individual particle diameters are not uniform). Is not very preferred. Also, those having a plurality of distribution peaks are not preferred.

(Conductivity measurement of this contact material and ABO ₃ system contact material)
The conductivity of the contact materials according to Examples 1 to 5 and the ABO ₃ contact material according to Comparative Example 1 obtained as described above was measured.

That is, a platinum paste was applied to both ends of an alumina rod (about 4.6 × 3.6 × 25 mm) and dried, and then a platinum lead wire was wound. Next, the contact material according to Examples 1 to 5 and the ABO ₃ system contact material according to Comparative Example 1 were thinly applied to one surface of this alumina rod, and then dried, and this test piece was connected to an AC impedance measuring device. Then, the electrical resistance (Ω) by the two-terminal method was measured. At this time, the measurement temperature and the heat history are 650 ° C. → 700 ° C. → 750 ° C. → 800 ° C. → 850 ° C. → 900 ° C. → 800 ° C. → 700 ° C. or the last 700 ° C. is not measured. It was.

Next, the conductivity was measured by the following formula.
Conductivity (S / cm) = (1 / measured electrical resistance (Ω)) × (length of material coated surface (cm) / cross-sectional area of material coated surface (cm ² ))

FIG. 1 shows the conductivity at each temperature. According to FIG. 1, the conductivity of the contact materials according to Examples 1 to 5 are all over the entire temperature range as compared with the conductivity of the ABO ₃ -based contact material according to Conventional Comparative Example 1. You can see that the rate is high.

  Moreover, it turns out that the electrical conductivity of the contact material which concerns on Examples 1-5 has improved as the mixing amount of the mixed powder of Ag powder and Pd powder increases. In particular, in Example 5 where the mixed powder of Ag powder and Pd powder was 70% by weight, it can be seen that the conductivity was improved to 800 S / cm.

  It can also be seen that the contact materials according to Example 3 and Example 4 in which the type of perovskite oxide is changed have substantially the same conductivity.

From the above, it can be seen that the present contact material is very excellent in electrical conductivity (low electrical resistance) as compared with the conventional ABO ₃ system contact material, and is extremely advantageous for improving the power generation performance of SOFC.

(Conductivity measurement of this contact material and silver-oxide contact material)
For the contact materials according to Examples 3 and 4 obtained as described above and the silver-oxide contact material according to Comparative Example 2, the conductivity was measured in the same manner as described above. At this time, the measurement temperature and the heat history were measured at 7 points of 650 ° C. → 700 ° C. → 750 ° C. → 800 ° C. → 850 ° C. → 900 ° C. → 800 ° C.

  FIG. 2 shows the conductivity at each temperature. According to FIG. 2, the electrical conductivity of the contact materials according to Examples 3 and 4 is over the entire temperature range as compared with the electrical conductivity of the silver-oxide based contact material according to the conventional Comparative Example 2. It can be seen that the conductivity is very high.

  However, it cannot be denied that the silver-oxide contact material cannot be evaluated correctly by the measurement method used this time. However, since the contact material for the air electrode is premised on being applied to the air electrode in a thin film, it is preferable that the conductivity is extremely low by the above measurement method in order to improve the power generation performance of the SOFC. It is thought that there is nothing.

(Production of SOFC and power generation test-1)
Next, SOFCs using contact materials according to the above examples and comparative examples were manufactured. That is, ScSZ having a 4 mol% Sc ₂ O ₃ -96 mol% ZrO ₂ composition (Daiichi Rare Element Chemical Co., Ltd., hereinafter referred to as “4ScSZ”) is used as a solid electrolyte material, and a binder is added to the slurry to form a slurry. A green sheet was prepared using a doctor blade method. Next, this green sheet was fired at 1350 ° C. for 2 hours to produce a solid electrolyte plate.

Next, as the fuel electrode material, NiO (manufactured by Nacalai Tesque) and ScSZ (manufactured by Daiichi Rare Element Chemical Co., Ltd.) having a composition of 10 mol% Sc ₂ O ₃ -1 mol% CeO ₂ -89 mol% ZrO ₂ , hereinafter referred to as “10Sc1CeSZ A binder (polyethylene glycol) was added thereto to form a slurry, which was applied to one surface of the solid electrolyte plate (thickness: about 25 μm) using a screen printing method. Subsequently, this was baked at 1350 degreeC for 2 hours, and it was set as the fuel electrode.

Next, La _0.6 Sr _0.4 (Co, Fe) O ₃ (manufactured by Seimi Chemical Co., Ltd.) is used as the air electrode material, and a binder (polyethylene glycol) is added to this to form a slurry, and screen printing is performed. It was applied to the other surface of the solid electrolyte plate (thickness: about 25 μm). Subsequently, this was baked at 1150 degreeC for 2 hours, and it was set as the air electrode.

Next, contact materials according to the above examples or comparative examples are shown in Table 1 below on the air electrode and separator on the air electrode side (made of stainless steel) of the obtained single cell (120 mmφ × 100 μm, electrode area about 100 cm ² ). The SOFCs according to Examples and Comparative Examples were produced by applying as shown and holding the single cell with a separator.

  Next, the power density at a power generation temperature of 800 ° C. was measured. At this time, hydrogen (flow rate: 1 L / min) was used as the fuel gas, and air (flow rate: 1 L / min or 2 L / min) was used as the oxidant gas. Table 1 shows the measurement results.

Next, using Table 1, the difference in power density (W / cm ² ) in each SOFC will be examined. In particular, in practical power generation, the value of the power density (W / cm ² ) near 0.7 V when using air is important, so this value will be considered.

According to Table 1, SOFC (No. 1) having an air electrode contact layer formed from a conventional ABO ₃ system contact material (Comparative Example 3), an ABO ₃ system contact material (Comparative Example 3), and a silver system contact material SOFC (No. 2) having an air electrode contact layer formed from (Comparative Example 5), SOFC (No. 3) having an air electrode contact layer formed from a silver-based contact material (Comparative Example 4), silver-based SOFC (No. 4) having an air electrode contact layer formed of a contact material (Comparative Example 4) and an ABO ₃ system contact material (Comparative Example 3) is about 0.126 to 0.224 (W / cm ² ). Output density.

On the other hand, in SOFC (No. 5) having an air electrode contact layer formed from the contact material (Example 3) according to this example, the output density is as high as 0.308 (W / cm ² ). The output density was about 1.4 to 2.4 times that of SOFC (No. 1 to 4). From this, it is understood that the SOFC (No. 5) according to the present invention has a very excellent power generation performance even in an air environment.

  Further, in the conventional SOFC (No. 3), the single cell and the separator were fixed by silver, and the single cell was cracked due to the difference in thermal expansion between the two. On the other hand, in the SOFC (No. 5) according to this example, no cracks occurred.

In addition, in the conventional SOFC (No. 2) and SOFC (No. 4), the ABO ₃ contact material and the silver contact material are separately applied and bonded to the air electrode and the separator. It can be seen that the power generation performance is not improved even if the air electrode contact layer is formed according to the configuration. That is, it can be seen that the Ag powder and the perovskite oxide powder do not contribute to the improvement of the power generation performance unless they are uniformly dispersed and mixed from the beginning like the contact material according to the present example.

(Production of SOFC and power generation test-2)
Next, SOFCs using contact materials according to the above examples and comparative examples were produced. That is, the same as in the above (SOFC production and power generation test-1-) except that a composite material of 0.5 wt% alumina (Al ₂ O ₃ ) with respect to 4ScSZ was used as the solid electrolyte material. Then, a single cell was produced, and the contact material according to the above example or comparative example was applied on the air electrode surface of the obtained single cell as shown in Table 2 below. The SOFCs according to the examples and comparative examples were produced by sandwiching with (made of stainless steel).

  Next, the power generation amount (W) at a power generation temperature of 800 ° C. was measured. At this time, hydrogen (flow rate: 1 L / min) was used as the fuel gas, and oxygen or air (flow rate: 1 L / min or 2 L / min) was used as the oxidant gas. Table 2 shows the measurement results.

  Next, using Table 2, the value of the power generation amount (W) near 0.7 V when oxygen or air is used will be examined.

  According to Table 2, SOFC (No. 6) having an air electrode contact layer formed from a conventional silver-oxide based contact material (Comparative Example 2) is 26.2 (W) under 1 L / min of oxygen. The power generation amount was 18.3 (W) under 1 L / min of air and 19.0 (W) under 2 L / min of air.

  On the other hand, in the SOFC (No. 7) having the air electrode contact layer formed from the contact material (Example 3) according to the present example, 37.8 (W), air 1 L / min under oxygen 1 L / min. 28.2 (W) under min and 29.8 (W) under air at 2 L / min, the amount of power generation is large under any condition, about 1.4 compared with the conventional SOFC (No. 6). It showed ~ 1.6 times the amount of power generation. Further, in SOFC (No. 8) having an air electrode contact layer formed from the contact material according to this example (Example 5), 36.6 (W) under 1 L / min of oxygen and 1 L / min under air. 28.7 (W), 30.2 (W) under 2 L / min of air, the power generation amount is large under any condition, and is about 1.4 to 1 compared with the conventional SOFC (No. 6). The power generation amount was 6 times.

  FIG. 3 shows the relationship between the IV curve and the power density of the conventional SOFC (No. 6) and the SOFC (No. 7) according to this example. According to FIG. 3, the SOFC according to this example has higher power generation performance than the SOFC according to the comparative example, not only in the oxygen environment but also in the air environment. In addition, although not shown in the figure, there was no reduction in output reduction over time.

  As described above, this SOFC having an air electrode contact layer formed from this contact material has extremely high power generation performance even in an air environment and does not cause destruction of a single cell. I can say that.

  The present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, the case where silver powder is used as the contact material for the air electrode is exemplified, but silver alloy powder can be used in addition to that. Moreover, although Pd powder was used as the noble metal powder, other noble metal powders or powders of noble metal alloys can be used. In addition, although the air electrode contact material is made into a paste state with a solvent, the air electrode contact material in which various powders are uniformly dispersed and mixed without using a solvent is also used as the air electrode in the powder state. It may be applied on the surface by a spray method or the like, and is not particularly limited.

It is the figure which showed the relationship between each temperature and electrical conductivity in the contact material which concerns on Examples 1-5 and the comparative example 1. FIG. It is the figure which showed the relationship between each temperature and electrical conductivity in the contact material which concerns on Example 3, 4 and the comparative example 2. FIG. It is the figure which showed the relationship between IV curve of conventional SOFC (No. 6) and SOFC (No. 7) which concerns on a present Example, and output density.

Claims (6)

  A contact material for an air electrode comprising at least silver powder or silver alloy powder and perovskite oxide powder.   The air electrode contact material further includes one or more selected from palladium (Pd), ruthenium (Ru), platinum (Pt), rhodium (Rh), iridium (Ir) and gold (Au). The contact material for an air electrode according to claim 1, comprising a noble metal powder or an alloy powder of the noble metal.   The air electrode contact material according to claim 1, wherein the air electrode contact material further contains a solvent.   The air electrode contact material according to claim 3, wherein the air electrode contact material further contains a resin.   5. The air electrode contact material according to claim 1, wherein the perovskite oxide is a lanthanum-cobalt oxide.   In the solid oxide fuel cell comprising a single cell in which a fuel electrode is joined to one surface of a solid electrolyte exhibiting oxygen ion conductivity and an air electrode is joined to the other surface through a separator, the multi-layered structure. 6. A solid oxide fuel cell, wherein an air electrode contact layer formed of the air electrode contact material according to claim 1 is interposed between an air electrode and the separator.

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