JP2014107063A - Single chamber type solid oxide ful cell and air electrode thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air electrode (cathode) of which the conductivity is high and which is unlikely to be destroyed even in a reduction atmosphere, and a single chamber type solid oxide fuel cell (SOFC) of which the power generation performance is improved relatively to the prior arts.SOLUTION: In an air electrode 18 of a single chamber type SOFC 10, a perovskite oxide such as LSTF with lower reduction expansion rate and conductivity is mixed with a perovskite oxide such as LSCF, and the two kinds of perovskite oxides with different physical properties are uniformly dispersed in entire tissues of the air electrode 18. Therefore, on the basis of containing the LSCF or the like with relatively high conductivity while entirely dispersing the LSCF, conductivity of the air electrode 18 is improved and on the basis of containing the LSTF or the like with the relatively low reduction expansion rate while entirely dispersing the LSTF, reduction durability of the air electrode 18 is improved. Therefore, the air electrode 18 can be obtained which is improves conductivity, is unlikely to be destroyed even in the reduction atmosphere, and is stably operated in the single chamber type SOFC 10.

Description

  The present invention relates to a single-chamber solid oxide fuel cell and an air electrode for constituting the same.

  A solid oxide fuel cell (SOFC) includes a solid electrolyte made of an oxide ion conductor, an air electrode (cathode), and a fuel electrode (anode). Oxygen is electrochemically reduced into oxygen ions that reach the fuel electrode via the electrolyte membrane. The oxygen ions oxidize the fuel gas such as hydrogen supplied on the fuel electrode to give electrons to the external load. Release and produce electrical energy. Such SOFCs have high power generation efficiency, low emissions of substances causing air pollution, low environmental impact, and the ability to use various fuels such as natural gas and coal gas. Therefore, development is progressing as a next generation power generator.

  A general SOFC has a laminated structure in which a solid electrolyte is sandwiched between an air electrode and a fuel electrode. The air electrode and the fuel electrode are made of a porous material having good gas diffusibility. As a solid electrolyte material, yttria-stabilized zirconia (YSZ) having a good balance of ion conductivity, stability and price is widely used.

In the laminated structure as described above, since the performance improves as the solid electrolyte becomes thinner, in recent years, development of an anode-supported SOFC in which the solid electrolyte is formed as a thin film on a fuel electrode porous substrate (that is, a fuel electrode support) Is progressing. In this structure, a mixture of NiO and YSZ (hereinafter referred to as NiO / YSZ) is generally used as the fuel electrode support material, and YSZ or the like is used as the solid electrolyte thin film material. In addition, as a constituent material of the air electrode formed on the solid electrolyte, perovskite oxides such as (La, Sr) CoO ₃ and (La, Sr) MnO ₃ are used.

  When the fuel electrode support is manufactured, for example, NiO / YSZ and a pore forming agent are mixed with a solvent / resin to form a slurry, which is then formed into a sheet by a doctor blade method or the like. A fuel electrode support layer can be obtained by applying an organic substance as an adhesive between the formed sheets or by thermocompression bonding and laminating so as to have a desired thickness of, for example, about 300 to 1000 (μm). On this fuel electrode support layer, an electrolyte layer, a reaction inhibition layer, and an air electrode layer are laminated by sheet printing so as to have a thickness of about 20 to 50 (μm) or by paste printing or the like, and fired. A single cell is obtained by processing. A fuel cell having a desired output can be obtained by stacking several tens of these via a separator to form a stack structure. At this time, the fuel gas (reducing gas) supplied to the fuel electrode and the oxygen (oxidizing gas) supplied to the air electrode are sealed with an interconnector or a sealing material so as not to mix. In addition, said reaction suppression layer is provided in order to suppress reaction of electrolyte and a cathode.

Japanese Unexamined Patent Publication No. 2000-243412 JP 2002-280015 A JP 2012-074307 A

  By the way, a single-chamber SOFC has been proposed for the purpose of simplifying the structure of the SOFC and providing it at low cost. In the single-chamber SOFC, no seal is provided between the fuel electrode and the air electrode, and power is generated with a mixed gas of fuel and air. Since the fuel electrode side is active in the fuel oxidation reaction, the fuel gas in the mixed gas is oxidized, and the air electrode side is inactive in the fuel oxidation reaction, so that the oxygen in the mixed gas is reduced. That is, power is generated by an electrochemical reaction similar to a conventional two-chamber structure in which a fuel electrode and an air electrode are separated. Such a single-chamber SOFC is expected to be a SOFC that can be manufactured at low cost, although its power generation performance is inferior to that of the two-chamber type because a mixed gas is used.

As an example of the single-chamber SOFC, for example, a fuel electrode made of nickel or a nickel-based metal oxide is provided on one side of a solid electrolyte, and (La, Sr) MnO ₃ or various metal oxides are provided on the other side. Some have an air electrode made of an added oxide (see, for example, Patent Document 1). The solid electrolyte is made of, for example, stabilized zirconia. The present invention proposes an electrode configuration that is less expensive than the conventional single chamber type in which Pd or Pt is required for the fuel electrode and Au is required for the air electrode.

As another example of the single-chamber SOFC, for example, on the same surface of the solid electrolyte, a fuel electrode composed of a double oxide mainly composed of nickel and cerium oxide, and (Ln, Sr) CoO ₃ (where Ln is There is one provided with an air electrode made of a rare earth element (see, for example, Patent Document 2). In the single-chamber SOFC as shown in Patent Document 1 above, electrodes are formed on both sides of the electrolyte, and it is necessary to make the electrolyte thin in order to obtain a high output, so that the strength cannot be obtained. The purpose is to satisfy both output and strength.

However, in a single-chamber SOFC, since a mixed gas is used, the air electrode is exposed to a reducing fuel gas. Therefore, materials with high conductivity such as (La, Sr) (Co, Fe) O ₃ , which have been conventionally used for air electrode materials in the two-chamber type, are currently used in reducing gas because of their high expansion coefficient. Since structural breakdown is likely to occur, it could not be used for the air electrode of a single-chamber SOFC. That is, since it is necessary to use a material with high reduction durability for the air electrode, the low electrical conductivity of the air electrode is also one of the causes of inferior power generation performance compared to the two-chamber type. In the present application, the reductive expansion coefficient is defined as [expansion coefficient in an atmosphere of 100% hydrogen gas] − [expansion coefficient in air]. The expansion rate in each atmosphere is measured in the temperature range from room temperature to 1000 (° C) using a thermomechanical analyzer (TMA), and the temperature range from room temperature to 700 (° C) determined from the results Is the value at.

  The present invention has been made in the background of the above circumstances, and the purpose thereof is an air electrode (cathode) that has high conductivity and is difficult to break even in a reducing atmosphere, and has superior power generation performance compared to the prior art. It is to provide a single-chamber SOFC.

  In order to achieve such an object, the gist of the first invention is an air electrode for constituting a single-chamber solid oxide fuel cell having a predetermined reduction expansion coefficient and a predetermined conductivity. A plurality of perovskite oxides each including a first perovskite oxide and a second perovskite oxide having a lower reductive expansion coefficient and lower conductivity than the first perovskite oxide. It is to have a structure consisting of dispersed exclusively perovskite type oxides.

  The gist of the single-chamber solid oxide fuel cell of the second invention is that the air electrode of the first invention, a predetermined fuel electrode, and an electrolyte provided between the air electrode and the fuel electrode, Is to include.

  According to the first aspect of the present invention, the air electrode includes a plurality of perovskite oxides including the first perovskite oxide and the second perovskite oxide having a lower reduction expansion coefficient and lower conductivity than the first perovskite oxide. Since it has a structure composed exclusively of perovskite type oxide dispersed, the conductivity of the air electrode is enhanced based on the fact that the first perovskite type oxide having a relatively high conductivity is dispersed throughout, and The reduction durability of the air electrode is enhanced based on the fact that the second perovskite oxide having a relatively low reduction expansion coefficient is dispersed throughout. That is, the first perovskite oxide forms a continuous or intermittent conductive path in the air electrode depending on the ratio, so that the first perovskite oxide is compared with the case where the entire structure is composed of the second perovskite oxide. Thus, the conductivity of the entire air electrode is enhanced according to the conductive path formed. In addition, since the thermal expansion of the first perovskite oxide in the reducing atmosphere is suppressed by the second perovskite oxide, the air is compared with the case where the whole is composed of the first perovskite oxide. The reductive expansion of the entire pole is suppressed. Therefore, it is possible to obtain an air electrode that has high conductivity and is difficult to break even in a reducing atmosphere and that operates stably with a single-chamber SOFC.

  Note that the conductivity and the reduction expansion coefficient of the entire air electrode are determined according to the respective conductivity, the reduction expansion coefficient, and the mixing ratio of the first perovskite oxide and the second perovskite oxide. Therefore, what is necessary is just to determine a material and a mixing ratio according to the desired characteristic. The conductivity of the entire air electrode is preferably 5 (S / cm) or more, and the reduction expansion coefficient is preferably 1 (%) or less.

  Further, according to the second invention, since the air electrode having the high conductivity of the first invention and not easily destroyed in the reducing atmosphere is used, reduction durability is required. Compared with the conventional single-chamber type SOFC in which the electrode is used, a single-chamber SOFC with excellent power generation performance can be obtained because it has a highly conductive air electrode. The “electrolyte provided between the air electrode and the fuel electrode” is suitable for the same surface as well as a laminated structure provided on different surfaces of the electrolyte so that the air electrode and the fuel electrode sandwich the electrolyte. Also includes structures provided at a distance.

Incidentally, in Patent Document 3, an air electrode is formed on one surface side of a solid electrolyte made of (La, Sr) (Ti, Fe) O ₃ and a fuel electrode is formed on the other surface side opposite thereto. In SOFC, the air electrode has a porous air electrode side reaction promoting layer, and the air electrode side reaction promoting layer has a skeleton structure made of (La, Sr) (Ti, Fe) O _3. The surface is impregnated with (La, Sr) (Co, Fe) O ₃ . (La, Sr) (Ti, Fe) O ₃ constituting this skeletal structure has a low reduction expansion coefficient and low conductivity compared to impregnated (La, Sr) (Co, Fe) O ₃ have. That is, the SOFC air electrode is composed of the first perovskite oxide and the second perovskite oxide having a lower reduction expansion coefficient and lower conductivity than the first perovskite oxide. Similar.

  However, the above SOFC is assumed to be used in the conventional two-chamber type and is not assumed to be used as a single-chamber type. The air electrode has a structure in which a void of a skeleton structure made of the second perovskite oxide is impregnated with the first perovskite oxide, and the first perovskite oxide is present on the surface of the air electrode. . Therefore, when this air electrode is exposed to a reducing atmosphere, the first perovskite oxide having a high reduction expansion coefficient is destroyed by the reduction expansion, and the conductive path is cut off. High power generation performance cannot be obtained. Therefore, this structure cannot be applied to a single-chamber SOFC in which the air electrode is exposed to a reducing atmosphere.

  In addition, the SOFC has the structure of the air electrode side reaction promoting layer made of the same material as that of the solid electrolyte so as not to cause problems such as interfacial delamination and element diffusion, but at least near the surface of the pores. Since the conductivity is improved by impregnating with a perovskite oxide having a high conductivity, the surface of the reaction promoting layer becomes dense. Therefore, in such a structure, there is also a disadvantage that the air electrode, which is preferably porous, becomes dense.

  Preferably, the first perovskite oxide has a conductivity of 200 (S / cm) or more and a reductive expansion coefficient of 1 (%) or more, and the second perovskite oxide is 100 It has a conductivity of (S / cm) or less and a reductive expansion coefficient of 0.4 (%) or less. In this way, since the first perovskite oxide has a sufficiently high conductivity, the conductivity of the air electrode is further enhanced, and the second perovskite oxide has a sufficiently low reduction expansion coefficient. Therefore, the reduction durability of the air electrode is further enhanced, and as a result, the power generation performance of the single-chamber SOFC having the air electrode is further enhanced.

Also, preferably, the first perovskite-type oxide is _{La 1-w Sr w Co 1} -x Fe x O 3 ( where, 0 <w <1,0 ≦ x ≦ 1), the second the perovskite type oxide is _{La 1-y Sr y Ti 1} -z Fe z O 3 ( where, 0 <y <1,0 <z <1). (La, Sr) (Co, Fe) O ₃ has a reduction expansion coefficient of, for example, 1 (%) or more and a conductivity of about 200 (S / cm), depending on the substitution ratios of both the A and B sites. (La, Sr) (Ti, Fe) O ₃ depends on the substitution rate of both A and B sites. For example, the reduction expansion coefficient is 0.4 (%) or less and the conductivity is 100 (S / cm) or less. Therefore, they can be suitably used as the first perovskite oxide and the second perovskite oxide, respectively.

The first perovskite-type oxide _{La 1-w Sr w Co 1} -x Fe x O 3 is preferably, Sr, replacement ratio w of Fe, x is 0 <w <a 0.5, 0 ≦ x ≦ 0.9 It is within the range. The second perovskite oxide La _1-y Sr _y Ti _1-z Fe _z O ₃ preferably has Sr and Fe substitution ratios y and z of 0 <y <0.5 and 0 ≦ z ≦. It is within the range of 0.95. (La, Sr) (Co, Fe) O ₃ has higher conductivity as Sr increases, but if it is too much, the reactivity with the cell member tends to increase, so w is preferably in the above range, 0.1 More preferably, ≦ w ≦ 0.4. Further, the oxygen reduction rate increases as Co increases, but the reduction expansion coefficient and the thermal expansion coefficient tend to increase. Therefore, x is preferably within the above range, and more preferably 0 ≦ x ≦ 0.8. In addition, (La, Sr) (Ti, Fe) O ₃ tends to have higher conductivity as Sr increases, so y is preferably in the above range, and more preferably 0.1 ≦ y ≦ 0.4. Further, since the reduction expansion coefficient and conductivity tend to decrease as the Ti content increases, a composition with a small Ti content is preferable. For example, 0.7 ≦ z ≦ 0.9 is preferable.

  Preferably, the air electrode contains the first perovskite oxide at a ratio of 20 (wt%) or more. In this way, since the first perovskite oxide having a high conductivity is sufficiently contained, higher conductivity can be obtained.

  Preferably, the air electrode contains the second perovskite oxide at a ratio of 20 (wt%) or more. In this way, since the second perovskite oxide having a low reduction expansion coefficient is sufficiently contained, higher reduction durability can be obtained.

  The first perovskite oxide and the second perovskite oxide are preferably contained in a proportion of 20 (wt%) to 80 (wt%).

  Preferably, the air electrode is a porous body formed by combining perovskite oxide particles, and the average particle diameters of the first perovskite oxide and the second perovskite oxide are , Respectively in the range of 0.05 to 5 (μm).

Preferably, the single-chamber solid oxide fuel cell includes a reaction suppression layer between the electrolyte and the air electrode. If the electrolyte is composed of a perovskite-based material that does not easily react with the perovskite oxide that forms the air electrode, the air electrode can be provided directly on one side of the electrolyte, but for example, the electrolyte is yttria stable. In the case of zirconia bromide (YSZ) or the like, it is preferable to provide a reaction suppression layer in order to suppress the reaction with the air electrode made of perovskite oxide. As the reaction suppression layer, for example, a layer made of ceria (GDC) doped with gadolinium is used. Ceria (CeO ₂ ) is a material with high ionic conductivity.In particular, GDC doped with gadolinium, which is an acceptor, is an excellent ionic conductor, so ionic conduction between the electrolyte and the air electrode. Therefore, it is preferable as a constituent material of the reaction suppression layer.

Preferably, the single-chamber solid oxide fuel cell is an anode-supported SOFC in which the fuel electrode supports an electrolyte and an air electrode. The constituent material of the fuel electrode is appropriately determined according to the desired characteristics.For example, a mixed material of NiO and 8YSZ (yttria-stabilized zirconia containing 8 (mol%) of Y ₂ O ₃ ) (hereinafter referred to as NiO / 8YSZ) Notation.). In addition, mixed materials such as CoO / 8YSZ, Co ₃ O ₄ / 8YSZ, FeO / 8YSZ, Fe ₂ O ₃ / 8YSZ, Fe ₃ O ₄ / 8YSZ, and the like can be given. The thickness dimension of the fuel electrode (anode support layer) in the case of adopting the above structure is, for example, 300 to 1000 (μm), and the thickness dimension of the air electrode is, for example, 20 to 50 (μm).

  The single-chamber solid oxide fuel cell may include an electrolyte support structure in which an air electrode and a fuel electrode are arranged on one surface of the electrolyte. Also in this structure, a reaction suppression layer can be provided between the electrolyte and the air electrode as necessary.

  Preferably, the air electrode comprises a plurality of kinds of perovskite oxide powders including a powder composed of the first perovskite oxide and a powder composed of the second perovskite oxide at a predetermined ratio. A mixing step in which the paste is mixed, a paste preparation step in which a solvent and an organic binder are added to the mixed powder to form a paste, and a coating step in which the paste is applied on the electrolyte or on a reaction suppression layer provided on one surface thereof. And a baking step of generating an air electrode from the coating film by performing a baking treatment.

  According to this configuration, the first perovskite oxide and the second perovskite oxide are mixed in a powder state, and the first perovskite oxidation is performed by applying the paste and applying and baking the paste. An air electrode composed of a perovskite oxide in which the product and the second perovskite oxide are dispersed is obtained. A method of forming an air electrode having a structure composed exclusively of perovskite type oxides in which a plurality of types of perovskite type oxides are dispersed is not particularly limited, but such powder mixing is simple and highly dispersed. It is preferable because of its property.

It is a figure which shows typically the layer structure of the single chamber type SOFC of one Example of this invention.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following embodiments, the drawings are appropriately simplified or modified, and the dimensional ratios, shapes, and the like of the respective parts are not necessarily drawn accurately.

  FIG. 1 is a diagram schematically showing a layer structure of a single-chamber SOFC 10 according to an embodiment of the present invention. In FIG. 1, a single-chamber SOFC 10 is a laminate in which an electrolyte 14, a reaction suppression layer 16, and an air electrode 18 are sequentially laminated on one surface of a fuel electrode 12.

  The fuel electrode 12 is a porous body made of a mixed material NiO / 8YSZ of NiO and 8YSZ, and has a large number of communicating pores extending from the surface (lower surface in FIG. 1) to the electrolyte 14. The mixing ratio of these NiO / 8YSZ is, for example, about NiO: 8YSZ = 6: 4 in mass ratio. The fuel electrode 12 has a thickness of about 300 to 1000 (μm), for example, and functions as a support for the single-chamber SOFC 10. Further, the porosity of the fuel electrode 12 is, for example, about 30 (%).

  The electrolyte 14 is a dense body made of 8YSZ and has a thickness dimension of about 10 (μm), for example.

  The reaction suppression layer 16 is made of 10 GDC (ceria doped with 10 (mol%) gadolinium) and has a relatively low porosity of, for example, about 5 to 10 (%). The thickness dimension of the reaction suppression layer 16 is, for example, about 5 (μm).

The air electrode 18 is made of a LaSr-based perovskite oxide. For example, (La, Sr) (Co, Fe) O ₃ (hereinafter referred to as LSCF as appropriate) and (La, Sr) ( It is a porous body made of a mixed material with Ti, Fe) O ₃ (hereinafter referred to as LSTF as appropriate), and has a large number of communicating pores extending from the surface (upper surface in FIG. 1) to the upper surface of the reaction suppression layer 16. ing. The mixing ratio of the LSCF and LSTF is, for example, about LSCF: LSTF = 2: 8 to 8: 2 in terms of mass ratio, and both are uniformly dispersed throughout the tissue of the air electrode 18 according to the mixing ratio. . These LSCFs and LSTFs can determine various substitution ratios at both the A and B sites. For example, (La, Sr) CoO ₃ (hereinafter referred to as LSC) or (La, Sr) FeO ₃ ( (Hereinafter referred to as LSF) can also be used. The air electrode 18 has a thickness dimension of about 20 to 50 (μm), for example, and has a porosity of about 20 to 30 (%), for example.

Among the mixed materials constituting the air electrode 18, LSCF, LSC, and LSF are materials having a relatively high conductivity and a high reductive expansion coefficient. For example, in La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ , 200 ( S / cm) and a reductive expansion coefficient of 1 (%) or more. LSTF is a material with relatively low electrical conductivity and low reductive expansion, and La _0.6 Sr _0.4 Ti _0.3 Fe _0.7 O ₃ has a conductivity of about 20 (S / cm) and a reductive expansion of about 0.1 (%). Rate. That is, in this embodiment, the air electrode 18 is composed of a mixed material of a perovskite oxide having a high reduction expansion coefficient and conductivity and a perovskite oxide having a lower reduction expansion coefficient and conductivity. Yes.

  The single-chamber SOFC 10 is manufactured, for example, as follows. First, a sheet (anode sheet) for forming the fuel electrode 12 is formed. That is, for example, NiO powder having an average particle diameter of about 0.5 (μm) and 8YSZ powder having an average particle diameter of about 0.5 (μm) are mixed at a mass ratio of, for example, 6: 4. As these NiO powder and 8YSZ powder, appropriate commercial products can be used. For this mixed powder 58 (wt%), xylene and other solvents 24 (wt%), methacrylate binder polymers and other organic binders 8.5 (wt%), carbon, starch and other pore forming agents (that is, carbon components) Add 5 (wt%) and 4.5 (wt%) plasticizer such as phthalate, and stir well to prepare a slurry. Using this slurry, a sheet molded body having a thickness of about 0.5 to 1.0 (mm) is molded by an appropriate sheet molding method such as doctor blade molding.

  Next, for 8YSZ 65 (wt%) with an average particle size of about 0.5 (μm), add solvent 31 (wt%) such as terpineol and organic binder 4 (wt%) such as ethylcellulose, and stir well. To prepare a paste. By using an appropriate printing technique such as screen printing, for example, a sheet molded body (electrolyte sheet) having a thickness of about 10 (μm) is obtained. This electrolyte sheet is laminated on the previously formed anode sheet.

  Next, a solvent 31 (wt%) such as terpineol and an organic binder 4 (wt%) such as ethyl cellulose are added to 10 GDC powder 65 (wt%) having an average particle size of about 0.5 (μm) A paste is prepared by kneading. By applying this paste on the above electrolyte sheet using an appropriate printing technique such as a screen printing method, a reaction suppression layer printed film is formed. The coating thickness is, for example, about 1 to 6 (μm).

  Next, the laminate of the anode sheet, the electrolyte sheet, and the reaction suppression layer printed film is fired in the air. The maximum holding temperature of the baking treatment is about 1350 (° C.). Thereby, a fired body in which the electrolyte 14 and the reaction suppression layer 16 are laminated on the fuel electrode 12 is obtained. At this time, since 10GDC constituting the reaction suppression layer 16 is a hardly sintered material, it cannot be sufficiently densified at the firing temperature, so that the pores of about 5 to 10 (%) remain as described above. It has become a thing.

  Next, an LSCF powder having an average particle size of about 1.0 (μm) and an LSTF powder having an average particle size of about 1.0 (μm) are prepared at a predetermined mixing ratio, and this powder 80 (wt% ), Add solvent 17 (wt%) such as terpineol, and organic binder 3 (wt%) such as ethylcellulose, and stir well to prepare a paste. That is, LSCF and LSTF are mixed in a powder state. This paste is applied with a thickness of, for example, about 20 to 50 (μm) on the reaction suppressing layer 16 of the fired body using an appropriate printing technique such as a screen printing method. This is fired in the atmosphere. The maximum holding temperature of the baking treatment is about 1100 (° C.). Thereby, the single-chamber SOFC 10 is obtained. Since the air electrode 18 of the single-chamber SOFC 10 is thus formed from a paste in which LSCF powder and LSTF powder are mixed, the LSCF and LSTF are uniformly distributed throughout the structure of the air electrode 18 as described above. It is distributed.

The single-chamber SOFC 10 configured as described above is installed in a predetermined container with leads attached to the fuel electrode 12 and the air electrode 18, and a mixed gas of fuel gas (for example, methane) and oxygen-containing gas (for example, air). Is caused to flow by flowing toward the single-chamber SOFC 10. The mixed gas is supplied onto both the fuel electrode 12 and the air electrode 18. On the fuel electrode 12 side, NiO / 8YSZ is active in the oxidation reaction of methane, and therefore the following reaction (1) occurs. On the other hand, since LSCF, LSTF, etc. are all inactive in the oxidation reaction of methane on the air electrode 18 side, the oxygen reduction reaction of (2) below occurs, and the generated oxygen ions are converted into the reaction suppression layer 16 and the electrolyte 14. To the fuel electrode 12. When an external load is connected between the fuel electrode 12 and the air electrode 18, electrons generated in the fuel electrode 12 by the following reaction flow through the external load. As described above, since the porosity of the reaction suppression layer 16 is low, air hardly permeates. However, 10GDC constituting this has excellent oxygen ion conductivity, so that it is between the electrolyte 14 and the air electrode 18. An oxygen ion conduction path through the reaction suppression layer 16 is formed.
^{_{(1) CH 4 + O 2-}} → CO + 2H 2 + 2e -
^{_{(2) O 2 + 4e -}} → 2O 2-

  Hereinafter, the results of evaluating the characteristics of the single-chamber SOFC 10 by variously changing the configuration of the air electrode 18 will be described together with comparative examples.

Table 1 below summarizes the characteristics evaluation results of the single-chamber SOFC 10. As the constituent material of the air electrode 18, La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ (indicated as LSCF in Table 1) and Examples A-1 to 5 in which La _0.6 Sr _0.4 Ti _0.3 Fe _0.7 O ₃ (indicated as LSTF in Table 1) was mixed at a mass ratio of 80:20 to 20:80, and a comparative example using no mixed material A-1 and A-2 are shown together. In Comparative Example A-1, the air electrode was composed only of LSCF, and in Comparative Example A-2, the air electrode was composed only of LSTF. In both the examples and comparative examples, the SOFC manufacturing method is the same as described above except that the air electrode material is different. Evaluation items are reduction expansion coefficient, reduction durability, thermal expansion coefficient, and 700 (° C.) performance. `` Reduction durability '' is determined by the temperature leading to breakage and peeling during use, `` X '' for 400 (° C) or less, `` △ '' for 600 (° C) or less, `` ○ '' for 900 (° C) or less, Samples that did not break or peel below 900 (° C) were marked with “◎”. “Thermal expansion coefficient” is a value in a temperature range from room temperature to 700 (° C.). "700 (° C) performance" is a mixed gas of methane (CH ₄ ) and air at 700 (° C), with gas flow rates of CH ₄ : 50 (ml / min), air: 200 (ml / min ) Is a measurement of power generation efficiency.

In Table 1 above, Examples A-1 to A-5, in which the air electrode 18 is made of a mixed material of LSCF and LSTF, are all sufficiently low in terms of the reduction expansion coefficient of less than 1 (%) and used at 700 (° C). It has a reduction durability. Moreover, since the power generation efficiency at 700 (° C.) is sufficiently high as 30 to 110 (mW / cm ² ), it can be put to practical use. The smaller the LSTF mixing ratio, the higher the reduction expansion coefficient and the higher the power generation efficiency. However, the higher the mixing ratio, the lower the reduction expansion coefficient, but the power generation efficiency decreases. Therefore, the mixing ratio is determined according to required durability and power generation efficiency.

On the other hand, Comparative Example A-1 in which the air electrode is composed only of LSCF has the result that the reductive expansion coefficient of the air electrode is as large as 1 (%) or more, and therefore breaks and peels at 400 (° C.) or less. It was. Therefore, although initially high power generation efficiency of about 120 (mW / cm ² ) can be obtained, it is not suitable as an air electrode of the single-chamber SOFC 10 because it has no reduction durability. Further, Comparative Example A-2 in which the air electrode is composed only of LSTF has a low reduction expansion coefficient of LSTF as low as 0.1 (%), so the reduction durability is extremely high, but the electric conductivity is low, so the power generation efficiency is low. Very low and not practical.

Table 2 below shows the physical properties of the air electrode material used in this example. In Table 2, “LSTF6419” is La _0.6 Sr _0.4 Ti _0.1 Fe _0.9 O ₃ , and “LSTF6437” is La _0.6 Sr _0.4 Ti _0.3 Fe _0.7 O ₃ . The LSTF used in the examples and comparative examples shown in Table 1 above is “LSTF6437” below, and the electrical conductivity is extremely low (20 (S / cm)). This alone is not suitable for use. In Table 2 below, “oxygen reducing ability” is the ability to reduce oxygen gas to oxygen ions. “Durability” means material stability such as structural stability at different oxygen partial pressures and reactivity with electrolytes and interconnector materials. In either case, ◎ is the best, and in the order of ○ △ ×.

Table 3 below uses La _0.6 Sr _0.4 Ti _0.1 Fe _0.9 O ₃ (LSTF6419 shown in Table 2 above) instead of La _0.6 Sr _0.4 Ti _0.3 Fe _0.7 O ₃ as a material to be mixed with LSCF. . The mixing ratio of LSCF and LSTF was 20:80 to 80:20 as shown in Table 1 above. In Table 3, for convenience, it is abbreviated as LSTF as in Table 1, but it is a different material from that used in Table 1.

Also in Examples B-1 to B-5, by using the air electrode 18 as a mixed material of LSCF and LSTF, a sufficiently high reduction durability as compared with Comparative Example B-1 of LSCF alone, and comparison of LSTF alone. A sufficiently high power generation efficiency is obtained as compared with Example B-2. In addition, La _0.6 Sr _0.4 Ti _0.1 Fe _0.9 O ₃ used in this evaluation has a reduction expansion coefficient of 0.4 (%), which is higher than La _0.6 Sr _0.4 Ti _0.3 Fe _0.7 O ₃ . Compared to the case, the degree of improvement in reduction durability is low with respect to the mixing ratio. Although only two types are shown in Table 2, LSTF tends to decrease in reduction expansion coefficient and conductivity as Ti increases. Therefore, in order to obtain the desired reduction durability and power generation efficiency, it is effective to consider the composition of LSTF.

Table 4 below shows evaluation results using La _0.6 Sr _0.4 CoO ₃ (hereinafter, LSC) instead of the LSCF used in Table 1. As shown in Table 2, LSC has a reductive expansion coefficient as high as 1 (%) or more, but has a very high electrical conductivity of 1200 (S / cm). Therefore, even if the air electrode 18 is composed of a mixed material of LSC and LSTF, both reduction durability and power generation efficiency can be achieved in the same manner as shown in Tables 1 and 3. Since LSC has the same oxygen reducing ability as LSCF, LSC is considered to have a slightly higher power generation efficiency because of its higher conductivity. In the low temperature range of 700 ° C. or lower, it is considered that the performance is higher when LSC is used. In general, the more lattice defects (that is, oxygen vacancies), the higher the catalytic activity and ionic conductivity. At lower temperatures, lattice defects are less likely to be formed, resulting in a decrease in both catalytic activity and ionic conductivity. Oxygen ions around Co are more likely to form lattice defects than oxygen ions around Fe because of the structure, but this difference becomes more noticeable at low temperatures, so LSC with a large amount of Co is relative to LSCF. In particular, the number of lattice defects increases, and as a result, the catalytic activity and ionic conductivity increase. For this reason, when LSC is used, higher performance is achieved at low temperatures.

  It should be noted that LSC has a higher reductive expansion coefficient than that of LSCF in which a part of Co at the B site is substituted with Fe, although it is similarly shown as “1 (%) or more” in Table 4. Therefore, in order to sufficiently increase the reduction durability of the mixed material, it is necessary to increase the mixing ratio of LSTF. When LSC: LSTF = 80: 20, the reduction durability is insufficient. That is, in this combination, the LSTF needs to be 30 (wt%) or more.

Table 5 below shows evaluation results using La _0.6 Sr _0.4 FeO ₃ (hereinafter, LSF) in place of the LSCF used in Table 1. As shown in Table 2, LSF has a reductive expansion coefficient as high as about 1.5 (%), but has a conductivity equivalent to 200 (S / cm) and LSCF. Therefore, even if the air electrode 18 is made of a mixed material of LSF and LSTF, both reduction durability and power generation efficiency can be achieved in the same manner as shown in Tables 1, 3, and 4. In this evaluation result, the power generation efficiency is inferior to the evaluation shown in Table 1, Table 3, and Table 4, but LSF has inferior oxygen reducing ability compared to LSC and LSCF because it lacks Co. This is probably because of this.

  As is clear from the above-described embodiments, according to this embodiment, the air electrode 18 of the single-chamber SOFC 10 is reduced to a perovskite oxide such as LSCF, LSC, LSF, etc. Perovskite type oxides such as LSTF with a low rate are mixed, and the perovskite type oxides having two different physical properties are uniformly dispersed in the entire structure of the air electrode 18, so that the conductivity is relatively high. The conductivity of the air electrode 18 is enhanced based on the fact that LSCF and the like are dispersed throughout, and the reduction of the air electrode 18 is based on the fact that LSTF and the like having a relatively low reduction expansion coefficient are dispersed throughout. Durability is increased. That is, since it is composed of a mixed material obtained by mixing two kinds of materials having contradictory characteristics, the air electrode 18 having both sufficiently high conductivity and reduction durability can be obtained. The mixing ratio of the two types of materials may be determined as appropriate based on the desired conductivity and reduction durability. As described above, the air electrode 18 that has high conductivity and is difficult to break even in a reducing atmosphere and operates stably in the single-chamber SOFC 10 can be obtained.

  Further, according to the present embodiment, since the air electrode 18 having high conductivity and not easily destroyed in the reducing atmosphere is used, the air electrode having low conductivity is used because reduction durability is required. Compared to the conventional single-chamber SOFC, since the air electrode 18 having high conductivity is provided, the single-chamber SOFC 10 having excellent power generation performance can be obtained. That is, by forming the air electrode 18 with a mixed material in which two kinds of materials having contradictory characteristics are mixed, a single-chamber SOFC 10 having sufficiently high power generation efficiency and reduction durability according to the mixing ratio thereof. Is obtained.

  As mentioned above, although this invention was demonstrated in detail with reference to drawings, this invention can be implemented also in another aspect, A various change can be added in the range which does not deviate from the main point.

10 Single-chamber SOFC
12 Fuel electrode 14 Electrolyte 16 Reaction suppression layer 18 Air electrode

Claims (4)

An air electrode for constituting a single-chamber solid oxide fuel cell,
A first perovskite oxide having a predetermined reduction expansion coefficient and a predetermined conductivity; and a second perovskite oxide having a lower reduction expansion coefficient and lower conductivity than the first perovskite oxide. An air electrode characterized in that a plurality of types of perovskite-type oxides including each have a structure composed exclusively of perovskite-type oxides.   The first perovskite oxide has a conductivity of 200 (S / cm) or more and a reduction expansion coefficient of 1 (%) or more, and the second perovskite oxide has a conductivity of 100 (S / cm) or less. The air electrode according to claim 1, wherein the air electrode has a conductivity and a reduction expansion coefficient of 0.4 (%) or less. The first perovskite-type oxide _{La 1-w Sr w Co 1} -x Fe x O 3 ( where, 0 <w <1,0 ≦ x ≦ 1) is, the second perovskite-type oxide The air electrode according to claim 1 or 2, wherein La _1-y Sr _y Ti _1-z Fe _z O ₃ (where 0 <y <1, 0 <z <1).   A single-chamber solid comprising the air electrode according to any one of claims 1 to 3, a predetermined fuel electrode, and an electrolyte provided between the air electrode and the fuel electrode. Oxide fuel cell.

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