JP2015088284A - Solid oxide fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an SOFC in which the exfoliation between a reaction suppression layer and an air electrode due to heat cycle is hard to occur and which has high power generation performance even by low temperature operation.SOLUTION: Since fine particles 20 having the same material as the air electrode 18 exist on the interface between a reaction suppression layer 16 and an air electrode 18, not only output is improved but only exfoliation due to heat cycle is suppressed, thereby obtaining an SOFC 10 suitable for low temperature operation at about 600 (°C). Furthermore, when the reaction suppression layer 16 is formed by a pulse laser deposition method, since the relative density is increased, cell impedance is further reduced and as a result, the output is improved at both 800 (°C) and 600 (°C).

Description

  The present invention relates to a solid oxide fuel cell having a structure including a reaction inhibiting layer between an electrolyte and an air electrode.

  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 to oxygen ions, which oxygen ions reach the fuel electrode via the electrolyte membrane, oxidize the fuel gas such as hydrogen supplied onto the fuel electrode, and 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 the solid electrolyte thin film material contains YSZ (especially 8YSZ, that is, 8 (mol%) of Y ₂ O ₃ ). Yttria stabilized zirconia) or the like is used. In addition, as a constituent material of the air electrode formed on the solid electrolyte, (La, Sr) CoO ₃ , (La, Sr) (Co, Fe) O ₃ , (La, Sr) MnO ₃ (hereinafter, LSC, Perovskite type oxides such as LSCF and LSM are used, but in such a combination, the solid electrolyte material and the air electrode material are likely to react, so in this type of SOFC, the reaction between these two layers Is provided with a reaction inhibiting layer (see, for example, Patent Document 3). For this reaction suppression layer, for example, gadolinium-doped ceria (hereinafter referred to as GDC), particularly 10GDC doped with 10 (mol%) of Gd 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.

  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.

JP 2005-339878 A Special table 2010-516035 gazette Japanese Patent No. 4913260

  By the way, the thermal expansion coefficient of GDC that constitutes the reaction suppression layer is about 12 (ppm), whereas the thermal expansion coefficient of perovskite oxides such as LSC and LSM that constitute the air electrode is about 17 (ppm). For this reason, the thermal expansion coefficients are significantly different. For this reason, when using SOFC, starting and stopping are repeated, so that there is a problem that peeling due to a heat cycle is likely to occur due to a difference in thermal expansion coefficient.

  Further, the operating temperature of a general SOFC is as high as about 700 to 1000 (° C.), and it is desired to lower it to about 500 to 600 (° C.). In high-temperature operation, by combining it with an energy recovery mechanism that uses waste heat, it is possible to obtain energy utilization efficiency as high as 70 to 80 (%) in the entire system. In addition, the ionic conductivity of the electrolyte and reaction suppression layer is higher at higher temperatures. Furthermore, since reforming fuel such as methane is an endothermic reaction, higher reforming efficiency can be obtained at higher temperatures. On the other hand, there are problems such as that the use is limited to large-scale power generation facilities, the start-up time is long, the heat-cycle easily deteriorates, and that the constituent materials are required to have high heat resistance. When the operating temperature is lowered, these problems are eliminated, and application to a distributed power source for home use, a power source for mobile electronic devices, an auxiliary power source for automobiles and the like can be expected.

  However, when the operating temperature is lowered, the ionic conductivity of the electrolyte and the reaction suppression layer is lowered and the overvoltage at the air electrode is increased, so that it is difficult to obtain practical power generation performance. In particular, the GDC that constitutes the reaction suppression layer is a hardly sintered material and has a low relative ionic conductivity because it remains at a relative density of about 90%, which also ensures power generation performance when the temperature is lowered. Make it more difficult. It is possible to increase the density by increasing the firing temperature when forming the GDC, but if the firing temperature of the GDC formed on the electrolyte is increased, the porosity of the fuel electrode support cannot be maintained. The cell impedance of the fuel cell is the sum of the ohmic resistance and the electrode overvoltage (that is, reaction resistance). The ohmic resistance increases as the ionic conductivity of the electrolyte and reaction suppression layer decreases. In addition, the overvoltage of the electrode, that is, the reaction resistance is a difficulty in causing an electrochemical reduction reaction.

  The present invention has been made against the background of the above circumstances, and an object of the present invention is to provide a SOFC in which separation between the reaction inhibition layer and the air electrode caused by heat cycle is unlikely to occur. Another object of the present invention is to provide a SOFC having high power generation performance even at low temperature operation.

  In order to achieve such an object, the gist of the present invention is a solid oxide fuel cell in which an electrolyte, a reaction inhibiting layer, and an air electrode are sequentially laminated on one surface of a fuel electrode, and (a) The object is to include a large number of fine particles having an average particle diameter of 5 to 100 (nm) distributed over the entire interface between the reaction suppression layer and the air electrode.

  In this way, since a large number of fine particles existing between the reaction suppression layer and the air electrode are fine, they easily bite into the surface of the reaction suppression layer and the air electrode, so that an anchor effect is obtained. Therefore, even if the thermal expansion coefficients of the reaction suppression layer and the air electrode are remarkably different, the peeling due to the heat cycle accompanying start / stop is suppressed. The average particle size of the above-mentioned many fine particles needs to be in the range of 5 to 100 (nm). If the average particle size is less than 5 (nm), the anchor effect is weak because it is too small. On the other hand, if it exceeds 100 (nm), it becomes difficult to maintain the independence between the fine particles, and the anchor effect is weakened because the film is formed. That is, in any case, it is difficult to suppress cracks and peeling at the interface between the reaction suppression layer and the air electrode.

  Here, preferably, the numerous fine particles are made of a ceramic material. In this way, even when the heat treatment for forming the air electrode is performed, the fine particles do not melt and the particles exist independently, so that a higher anchor effect can be obtained.

  Preferably, the many fine particles are made of the same material as the air electrode. In this way, since a large number of fine particles substantially form part of the air electrode, the contact interface between the air and the air electrode supplied during operation is substantially increased by the large number of fine particles. The oxygen reduction performance of the air electrode is enhanced. In addition, many fine particles present at the interface between the reaction suppression layer and the air electrode are the same material as the air electrode, and therefore do not hinder ion conduction between them. Rather, the presence of fine particles in the gaps that may occur due to surface irregularities and the porosity of the air electrode at the interface between them forms an ion conduction path between them, so that the ion conductivity is reduced. Enhanced. Furthermore, although it seems that the fine particles of the air electrode material are highly active in reducing oxygen, the reaction resistance of the air electrode, that is, overvoltage is suppressed even at low temperature operation. For this reason, even if a large number of fine particles are present at the interface between the air electrode and the reaction suppression layer, there is no performance degradation due to this. Instead, the oxygen reduction performance is improved, the ion conductivity is improved, and the overvoltage is suppressed at a low temperature. SOFC with high power generation performance can be obtained even at low temperature operation.

  Preferably, the reaction suppression layer is composed of GDC. GDC is a preferred material for the reaction suppression layer because of its high ionic conductivity, but tends to have a lower thermal expansion coefficient than an air electrode material having a high oxygen reduction activity. For example, the thermal expansion coefficient of LSC, LSCF or the like generally used as an air electrode material is about 17 (ppm), whereas the thermal expansion coefficient of GDC is about 12 (ppm). Therefore, since the thermal expansion coefficients are remarkably different from each other in this way, the reaction suppression layer and the air electrode are easily separated in the heat cycle in use, and thus the separation suppression effect due to the provision of the fine particles at their interface is more remarkable. Is obtained.

  Preferably, the reaction suppression layer has a relative density of 95 (%) or more. In this way, since the density of the reaction suppression layer is sufficiently increased, higher ion conductivity can be obtained. Therefore, sufficiently high power generation performance can be obtained even if the operating temperature is lowered to, for example, about 500 to 600 (° C.). Since ion conductivity generally decreases as the temperature decreases, high temperature operation of about 700 to 1000 (° C) is sufficient to obtain sufficiently high ion conductivity even at a low relative density of 90 (%) or less. High power generation performance can be obtained. However, in low-temperature operation of about 500 to 600 (° C.), such low density has low ion conductivity and power generation performance cannot be obtained. In addition, it is considered that when the relative density is increased, the smoothness of the surface is improved, so that the reaction-suppressing layer and the air electrode are more easily separated. According to the present invention, the nanoparticles present at the interface Peeling is sufficiently suppressed by the anchor effect.

  Preferably, the reaction suppression layer is formed by a pulse laser deposition method. In this way, a reaction inhibiting layer having a relative density of 95 (%) or more can be easily obtained without requiring a high-temperature baking treatment. That is, GDC was conventionally formed by slurry application and firing as shown in the above-mentioned Patent Document 3 and the like, but in this method, the relative density was 90% or less as described above. The relative density can be increased by increasing the firing temperature to, for example, 1500 (° C.) or more.However, while maintaining the porosity of the fuel electrode, a solid solution layer is generated due to the reaction between the electrolyte and the reaction suppression layer, resulting in resistance. In order to suppress the increase in the thickness, it is preferable to keep the firing temperature at 1400 (° C.) or lower, and thus the relative density could not be increased. According to the above aspect, a high density of 95 (%) or more can be easily obtained, and film formation at a lower temperature is possible than before, so that the interface resistance between the electrolyte and the reaction inhibition layer is reduced. Can do.

  Preferably, the large number of fine particles are formed by a pulse laser deposition method. In this way, the fine particles can be easily formed, and the fine particles formed by the pulse laser deposition method are firmly fixed to the formation surface, so that a high anchor effect can be obtained.

  Incidentally, the above-described pulsed laser deposition method has been widely used in the SOFC field, and for example, a thin film made of a material having higher electron conductivity than that of each of the fuel electrode and the air electrode is used. In some configurations provided as a current collecting layer, the current collecting layer is formed by a pulsed laser deposition method (see, for example, Patent Document 1). In the above configuration, the pulse laser deposition method is shown as an example of a thin film forming method. As the constituent material of the current collecting layer, conductive oxides (for example, ITO, ZnO, Ga-added ZnO, etc.), conductive nitrides (for example, TiN, TiAlN, etc.), conductive carbides, alloys containing Ni or Fe Materials (for example, FeCrAl, FeCrSi, FeCrW, etc.), noble metals and alloy materials (for example, Pt, Pd, Ru, Ag, etc.) containing them are mentioned. In addition, in a configuration in which the cathode provided on one surface of the electrolyte layer includes a high-density ion-electron mixed conductor (MIEC) thin film, the electrolyte layer and the MIEC thin film were formed by a pulse laser deposition method. Some (see, for example, Patent Document 2).

  As described above, the pulse laser deposition method is conventionally known, and it is well known that a dense film can be easily formed without misalignment by using this method. There is no example applied to the provided structure, and there is no example used for fine particle formation in SOFC. The present inventors have found that nanoparticles can be formed by appropriately adjusting the laser output, frequency, temperature, gas partial pressure, number of shots, etc. when using the pulsed laser deposition method, and the present invention is based on such knowledge. It was made based on.

  The method for forming the reaction suppression layer and the fine particles may be appropriately selected so that a desired film and fine particles are formed, and is not limited to the above-described pulse laser deposition method. For example, a film forming method such as sputtering or CVD can be applied. In the case of the pulsed laser deposition method, the particle diameter is determined according to each of the above conditions. For example, the particle diameter increases as the number of shots increases, so for example, about 50 to 500 times depending on the desired particle diameter. The number of shots may be determined within the range of Although other conditions also affect, as the number of shots increases, it becomes easier to form a film and it becomes difficult to maintain the state of individually separated particles.

The constituent material of the air electrode is not particularly limited, but (La _1-x Sr _x ) (Co _1-y Fe _y ) O _3-δ (where 0 <x <1, 0 ≦ y <1, 0 ≦ δ <1), La (Ni _1-x Fe _x ) O _3-δ (where 0 <x <1, 0 ≦ δ <1), (Sm _1-x Sr _x ) CoO _3-δ (where 0 <x <1, 0 ≦ δ <1) and the like. In the SOFC to which the present invention can be applied, the constituent material of each layer is not particularly limited. For example, the air electrode material is preferably LSCF, La (Ni _1-x Fe _x ) O _3-δ, or the like. In particular, since LSC and LSCF have high ionic conductivity, high power generation performance can be obtained.

The constituent material of the electrolyte is not particularly limited.For example, 8YSZ, 10ScSZ (scandia-stabilized zirconia containing 10 (mol%) Sc ₂ O ₃ ), (La _1-x Sr _x ) (Ga _1-y Mg _y ) O _3−δ (where 0 <x <1, 0 ≦ y <1, 0 ≦ δ <1) and the like. In the combination of the air electrode material and the electrolyte material, a high resistance layer is easily formed by reaction, and thus the reaction suppression layer is essential. The present invention is suitably applied to a combination of constituent materials that require such a reaction inhibiting layer.

The constituent material of the fuel electrode is not particularly limited. For example, in addition to the NiO / 8YSZ, CoO / 8YSZ, Co ₃ O ₄ / 8YSZ, FeO / 8YSZ, Fe ₂ O ₃ / 8YSZ, Fe ₃ O ₄ / Examples thereof include mixed materials such as 8YSZ and perovskite oxides such as (La _1-x Sr _x ) TiO ₃ (where 0 <x <1, 0 ≦ δ <1).

  Preferably, the fuel electrode is an anode supporting layer that functions as a SOFC supporting layer. The present invention is suitably applied to such an anode-supported SOFC. In the case of having such a structure, the thickness dimension of the fuel electrode (anode support layer) is, for example, 300 to 1000 (μm), and the thickness dimension of the air electrode is, for example, 20 to 50 (μm). .

Preferably, the SOFC has an impedance temperature change rate obtained by the following equation (1) from a value Z _{600 at 600} (° C.) and a value Z _{800 at} 800 (° C.) of the impedance measured by the electrochemical impedance method. 160 (%) or less. As described above, when the operating temperature is lowered, the ionic conductivity of the electrolyte and the reaction suppressing layer is lowered, and the overvoltage at the air electrode is increased, so that the impedance of the cell is increased. If the impedance temperature change rate is large, it will be difficult to obtain power generation performance at low temperatures, but by keeping the temperature change rate below 160 (%), power generation is sufficiently high even at low temperatures of about 500 to 600 (° C). Performance is obtained. According to the present invention, since the fine particles made of the same material as the air electrode present at the interface between the reaction suppression layer and the air electrode are highly active in reducing oxygen, an increase in overvoltage of the air electrode is suppressed. Impedance temperature change rate is reduced. In particular, in a mode in which the reaction suppression layer is formed at a relative density of 95 (%) or higher, the temperature change rate of impedance is further suppressed by increasing its ionic conductivity, so that higher power generation performance can be obtained. it can. In addition, the said electrochemical impedance method measures using a potentiostat and a frequency response analyzer in the frequency range of 1 (MHz)-0.1 (Hz), for example.
[(Z ₆₀₀ −Z ₈₀₀ ) / Z ₈₀₀ ] × 100 (%) (1)

  Preferably, the large number of fine particles have an average particle size of 1/40 to 1/10 of the crystal particle size of the reaction suppression layer. In this way, a higher anchor effect can be obtained, and an increase in the overvoltage of the air electrode can be further suppressed to further reduce the impedance. When the fine particle diameter is less than 1/40 of the crystal grain size of the reaction suppression layer, the effect of increasing the contact area is reduced and the effect of reducing the impedance is reduced. On the other hand, if it exceeds 1/10, the amount of biting into the surface of the reaction inhibiting layer is reduced, the anchor effect is reduced, and the peeling inhibiting effect is reduced.

  Preferably, the SOFC of the present invention is produced, for example, by the following steps. That is, a lamination process for producing a laminate in which an electrolyte membrane is laminated on a fuel electrode support and a reaction inhibition layer is laminated on the electrolyte membrane, and distributed over the entire surface of the reaction inhibition layer of the laminate. Are manufactured by a manufacturing process including a fine particle forming step in which a large number of fine particles are provided by a pulse laser deposition method and an air electrode stacking step in which an air electrode is formed on the large number of fine particles. According to the pulsed laser deposition method, the particle size can be easily controlled by appropriately adjusting the laser output, frequency, temperature, gas partial pressure, number of shots, etc., so that the fine particles having a desired particle size on the reaction suppression layer Can be easily formed. For this reason, it is possible to obtain an appropriate biting state of the fine particles with respect to the reaction suppression layer and the air electrode, so that a sufficient anchor effect can be obtained.

  Preferably, the fine particle forming step forms fine particles of the same material as the air electrode on the reaction suppression layer. According to the pulse laser deposition method, a film or particle having a desired composition can be easily formed without composition deviation. Therefore, by forming fine particles of the same material as the air electrode, the fine particles form a part of the air electrode, so that a new ion conduction path is formed and the air electrode material fine particles highly active in reducing oxygen Due to the presence of the air electrode overvoltage is suppressed even at low temperature operation. As a result, an SOFC having high power generation performance even at low temperature operation can be obtained.

  Preferably, the laminating step includes a reaction inhibition layer forming step of forming the reaction inhibition layer on the electrolyte film by a pulse laser deposition method. According to the pulse laser deposition method, a dense film can be easily formed. Thus, in this way, the relative density of the reaction suppression layer is increased and the ionic conductivity is increased compared to the case of printing. Thus, the power generation performance can be improved. In particular, when the constituent material of the reaction suppression layer is GDC, the relative density in the case of printing and forming has remained at about 90 (%), whereas a high relative density of about 98 (%) can be obtained. Therefore, the ionic conductivity inherent to the material can be exhibited and higher power generation performance can be obtained.

It is a figure which shows typically the layer structure of the anode support type | mold SOFC of one Example of this invention. It is a figure which expands and shows typically the interface of the SOFC reaction suppression layer of FIG. 1, and an air electrode. It is process drawing explaining the manufacturing method of SOFC of FIG. FIG. 4 is an SEM image showing a state in which a large number of fine particles are formed on the surface of the reaction suppression layer by the fine particle formation step of FIG. 3. It is a SEM image which expands and shows the center part of FIG. It is a graph which shows the impedance measurement result of SOFC of an Example.

  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 an anode-supported SOFC 10 according to an embodiment of the present invention. In FIG. 1, the SOFC 10 is a laminated body 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 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 an extremely high relative density of about 95 (%) or more, for example, about 98 (%). It has a thermal expansion coefficient of about 12 (ppm). The thickness dimension of the reaction suppression layer 16 is, for example, about 5 (μm).

In addition, the air electrode 18 includes, for example, (La, Sr) CoO ₃ (for example, La _0.6 Sr _0.4 CoO ₃ ; hereinafter referred to as LSC as appropriate), (La, Sr) (Co, Fe) O ₃ (for example, La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ (hereinafter referred to as LSCF as appropriate) and the like, and a porous body made of a perovskite oxide containing La, Sr, Co, etc., and its reaction inhibiting layer from its surface (upper surface in FIG. 1) It has many communicating pores that continue to the top surface of 16. These LSC and LSCF can determine various substitution ratios at both the A and B sites, and those having an appropriate substitution ratio can be used depending on the desired ion conductivity, reduction expansion coefficient, and the like. The air electrode 18 has a thickness of about 20 to 50 (μm), for example, has a porosity of about 20 to 30 (%), and a thermal expansion coefficient of about 17 (ppm), for example. It is.

The LSC and LSCF constituting the air electrode 18 are materials having relatively high electronic conductivity and ionic conductivity and having a relatively large reduction expansion coefficient. For example, La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ has an electronic conductivity of about 200 (S / cm) and a reduction expansion coefficient of 1 (%) or more.

  In addition, between the reaction suppression layer 16 and the air electrode 18, a large number of fine particles 20 are distributed throughout the interface, as schematically shown in FIG. The fine particles 20 are made of the same material as the air electrode 18, that is, a perovskite oxide such as LSC and LSCF, and are nanoparticles having a particle diameter in the range of 5 to 100 (nm), for example, about 50 (nm). is there. The fine particles 20 are fixed to the reaction suppression layer 16, and a portion protruding from the reaction suppression layer 16 bites into the air electrode 18. As a result, the reaction suppression layer 16 and the air electrode 18 are in direct contact with each other and partially in contact with each other through the fine particles 20. Further, the upper surface of the reaction suppression layer 16 and the lower surface of the air electrode 18 are not necessarily flat, and there are irregularities as schematically shown in FIG. 2, and gaps due to the irregularities are also generated.

The 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 the cell temperature is maintained at a predetermined operating temperature, for example, about 500 to 800 (° C.). Electricity is generated by flowing an oxygen-containing gas, such as air, on the air electrode 18 side and a hydrogen-containing gas on the fuel electrode 12 side. For example, when the cell temperature is operated under the condition of 800 (° C), a high output of about 1.0 (W / cm ² ) or more is obtained.For example, even when operated under the condition of 600 (° C), 0.5 to 0.6 (W A sufficiently high output of about / cm ² ) can be obtained. Moreover, the operating time for one operation is about 20 hours, and the temperature is raised and lowered at 400 (° C / h) between the operating state of 600 (° C) and the stopped state of 200 (° C), and starting and stopping 50 times or more Even if it repeats, peeling of the reaction suppression layer 16 and the air electrode 18 is not recognized at all, and it has a practical long life. Since the output of one cell of the SOFC 10 is relatively small as described above, when using it as a power generation device, for example, a plurality of cells are stacked to form a stack structure, and a plurality of such cell stacks are combined. One device is configured.

  According to this embodiment, since there are a large number of fine particles 20 having a particle diameter of about 5 to 100 (nm) at the interface between the reaction suppression layer 16 and the air electrode 18, the fine particles 20 are the air electrode 18. The anchor effect is obtained by biting into the surface. Therefore, the thermal expansion coefficient of the reaction suppression layer 16 is about 12 (ppm) and the thermal expansion coefficient of the air electrode 18 is about 17 (ppm). The peeling due to the heat cycle accompanying the start / stop is suppressed.

  In addition, since the fine particles 20 are made of the same material as the air electrode 18, the large number of fine particles 20 substantially constitute a part of the air electrode 18, so that the air supplied during operation and the air electrode 18 Since the contact interface is substantially increased by the large number of fine particles 20, the oxygen reduction performance of the air electrode 18 is enhanced. Moreover, since the numerous fine particles 20 present at the interface between the reaction suppression layer 16 and the air electrode 18 are made of the same material as the air electrode 18, ion conduction between them is not inhibited at all, On the other hand, since a new ion conduction path is formed, ion conductivity is improved. Furthermore, the fine particles 20 of the air electrode material are considered to suppress the overvoltage of the air electrode 18 in the low temperature operation. It is considered that the high output as described above can be obtained by these.

  FIG. 3 is a process diagram illustrating an example of a method for manufacturing the SOFC 10 described above. In FIG. 3, in the anode sheet forming step P1, for example, a commercially available NiO powder having an average particle size of about 0.5 (μm) and a commercially available 8YSZ powder having an average particle size of about 0.5 (μm) are used, for example, 6: 4. The mixed powder 58 (wt%) was mixed with a solvent such as xylene 24 (wt%), an organic binder such as a methacrylate polymer 8.5 (wt%), carbon, starch and other pores. Add 5 (wt%) of the forming agent (namely, carbon component) and 4.5 (wt%) of a plasticizer such as phthalate, and prepare a slurry by stirring well. From this slurry, a sheet molded body (anode sheet) having a thickness dimension of about 0.5 to 1.0 (mm) is molded by an appropriate sheet molding method such as doctor blade molding.

  Next, in the electrolyte sheet forming step P2, the same 8YSZ powder 60 (wt%) as used in the step P1 is added to an alcoholic solvent 36 (wt%) such as terpineol and an organic binder 4 such as ethylcellulose. (wt%) and add well to prepare a paste. From this paste, a sheet molded body (electrolyte sheet) having a thickness dimension of about 10 (μm) is obtained by an appropriate thick film forming technique such as a screen printing method. In the anode / electrolyte stacking step P3, the anode sheet is stacked on the electrolyte sheet thus obtained to obtain an electrolyte / anode sheet stack.

  Next, in the firing step P4, the electrolyte / anode sheet laminate is subjected to a firing treatment, that is, co-firing. The maximum holding temperature of the baking treatment is, for example, about 1350 (° C.). As a result, the electrolyte 14 and the fuel electrode 12 are generated from the electrolyte sheet and the anode sheet, respectively, and a fuel electrode / electrolyte laminate is obtained.

Next, in the reaction inhibition layer forming step P5, the fuel electrode / electrolyte laminate is placed in a predetermined chamber, and a GDC film (that is, the reaction inhibition layer 16) is formed on the electrolyte 14 by a pulse laser deposition method. The conditions for forming the GDC film are, for example, a substrate temperature of 700 (° C.), a laser fluence of 10 (kJ / m ² ), a frequency of 10 (Hz), an oxygen partial pressure of 5 (Pa), and about 30000 shots. In the chamber, a constituent material of a film to be formed, in this embodiment, a GDC target is arranged. This target is, for example, a pellet obtained by press-molding a raw material having an average particle size of about 0.3 (μm) and firing at 1500 (° C.). As a result, 10 GDC having a thickness dimension of about 5 (μm) is formed on the electrolyte 14 and firmly adhered to the formation surface. According to the pulse laser deposition method, a dense film having a desired composition can be easily formed.Therefore, there is no composition deviation equal to or higher than that in the case of printing formation, and as described above, a high density of about 98 (%). A 10GDC membrane can be obtained. In addition, the said substrate temperature is suitably set between 500-1000 (degreeC). If it is too low, no oxide is produced, and if it is too high, it reacts with YSZ constituting the electrolyte 14 to form a resistance layer. The laser fluence is appropriately set between 0.1 and 30 (kJ / m ² ). If it is too low, the material will not fly on the substrate, and if it is too high, the film cannot be formed uniformly. The oxygen partial pressure is appropriately set in the range of 0.01 to 100 (Pa), but if it is too low, oxides cannot be formed.

Next, in the fine particle formation step P6, the nanoparticles (that is, the fine particles 20) made of LSC are formed using the pulse laser deposition method while the stacked body on which the reaction suppressing layer 16 is formed is placed in the chamber. The formation conditions of the nanoparticles are, for example, a substrate temperature of 700 (° C.), a laser fluence of 10 (kJ / m ² ), a frequency of 10 (Hz), an oxygen partial pressure of 30 (Pa), and a shot count of 50 to 500. The number of shots varies depending on the particle size of the fine particles 20 to be formed. As described above, when forming the fine particles 20 having a particle size of about 50 (nm), the number of shots is about 200. In the chamber, a constituent material of the fine particles 20 to be formed, an LSC target in this embodiment, is arranged. This target is a pellet obtained by press-molding an LSC raw material and firing at about 1200 (° C.). As a result, a large number of fine particles 20 (nanoparticles) having a desired average particle diameter are formed on the reaction suppression layer 16 and firmly adhered to the formation surface. According to such a pulse laser deposition method, nanoparticles having the same size can be formed without composition deviation, and therefore, fine particles 20 having the same composition as the air electrode 18 can be easily obtained. In this fine particle formation, the substrate temperature is appropriately set between 500 and 1000 (° C.). If it is too low, no oxide is produced, and if it is too high, diffusion is too fast and particles are not formed to form a film. The laser fluence is appropriately set between 0.1 and 30 (kJ / m ² ). If it is too low, the material will not fly onto the substrate, and if it is too high, particles will not be formed. The oxygen partial pressure is appropriately set in the range of 0.01 to 100 (Pa), but if it is too low, oxides cannot be formed.

  4 is an SEM image of the surface of the reaction suppression layer 16 after the formation of the fine particles 20 described above, and FIG. 5 is an enlarged SEM image of the central portion of FIG. The surface of the reaction suppression layer 16 is an uneven surface on which a grain boundary of GDC appears, and countless points that appear whitish in the SEM image are the fine particles 20. As shown in FIG. 4, the fine particles 20 are uniformly distributed in a state where the fine particles 20 are sufficiently exposed on the surface of the reaction suppressing layer 16, and there is little overlap between the particles, but some particles have a plurality of particles. It sticks to a film. Further, as shown in FIG. 5, each particle of the fine particles 20 has an angular portion, but is generally spherical.

  Returning to FIG. 3, in the cathode printing layer forming step P7, for example, a commercially available LSCF powder 80 (wt%) having an average particle diameter of about 1.0 (μm) is added to an alcohol solvent 16 (wt%) such as terpineol. Then, an organic binder 4 (wt%) such as ethyl cellulose is added and sufficiently stirred to prepare a paste. This paste is applied on the reaction suppression layer 16 of the laminate in which the fine particles 20 are formed with a thickness of, for example, about 20 to 50 (μm) by an appropriate thick film forming technique such as a screen printing method. In the firing step P8, the laminate is subjected to a firing process at a maximum holding temperature of, for example, about 1100 (° C.), whereby the air electrode 18 is formed from the printed film, and the SOFC 10 is obtained. Since the fine particles 20 are provided in a state where the surface of the reaction suppression layer 16 is sufficiently exposed as described above, the air electrode 18 formed in this way is generally provided directly on the reaction suppression layer 16. Is in a state.

  Table 1 below shows the results of evaluating the SOFC 10 of the present embodiment by variously changing the formation method of the reaction suppression layer 16 and the particle size of the fine particles 20 together with the evaluation results of the comparative example in which the fine particles 20 are not provided. It is shown.

  In Table 1 above, Example 4 is based on the configuration and manufacturing method described above. In addition, Example 1 is configured in the same manner as Example 4 except that the reaction inhibition layer 16 is formed by printing. In Example 1, following the anode / electrolyte lamination step P3 shown in FIG. 3, a GDC paste is applied on the electrolyte sheet by a screen printing method to a thickness of 1 to 6 (μm), for example, 1350 (° C. The fuel electrode 12, the electrolyte 14, and the reaction suppression layer 16 are co-fired by performing a baking process at the maximum holding temperature. The GDC paste is, for example, a commercially available 10GDC powder 65 (wt%) having an average particle size of about 0.5 (μm), an alcoholic solvent 31 (wt%) such as terpineol, and an organic binder 4 (wt%) such as ethylcellulose. ) Is added and kneaded thoroughly.

  Examples 2, 3 and 5 were manufactured in the same process as in Example 4, but the particle size of the fine particles 20 was changed to 5 to 100 (nm) by changing the number of shots in the fine particle forming step P6. ) Is different within the range. For example, the number of shots in each example is 50 in Example 2, 100 in Example 3, and 500 in Example 5.

  Further, Comparative Example 1 has a conventional configuration in which the reaction suppression layer 16 is printed and formed in the same manner as in Example 1 and the fine particles 20 are not provided. In Comparative Example 2, the reaction suppression layer 16 is formed by the pulse laser deposition method, but the fine particles 20 are not provided. In Comparative Example 3, the reaction suppression layer 16 is formed by a pulse laser deposition method, but a film is formed on the reaction suppression layer 16 instead of the fine particles 20. The comparative example 3 is manufactured through the same process as that of the fourth embodiment. However, since the number of shots when forming the fine particles 20 by the pulse laser deposition method is large, for example, about 1000 times, the particles are bonded to each other. Thus, an LSC film is formed.

Also, in Table 1, “800 (° C.) output” and “600 (° C.) output” both use a commercially available fuel cell evaluation device (for example, a Chino fuel cell evaluation device) and the cell temperature is 800 (° C.) and 600 (° C.) are set to evaluate the output. In the measurement, the cell area was φ20 (mm), the cathode area was φ10 (mm), H ₂ : 50 (ml / min), Air: 100 (ml / min) was supplied to the cell to generate electricity. Moreover, Pt mesh was used for current collection.

  In addition, “cell impedance” means impedance using a potentiostat and frequency response analyzer (manufactured by Toyo Technica Co., Ltd.) in the frequency range of 1 (MHz) to 0.1 (Hz) under the 600 (° C) cell driving conditions of the power generation cell. Is obtained from the result of continuous measurement. FIG. 6 shows an example of the measurement result. In the figure, the impedance from the Z ′ axis labeled “cell impedance” to the intersection with the Z ′ axis of the plot is defined as the impedance of the measurement target cell.

  “800 ° C. → 600 ° C. impedance temperature change rate” is obtained by the above equation (1) from the impedance value measured at 600 (° C.) and 800 (° C.) as described above. is there. In general, when the operating temperature is lowered, the ionic conductivity of the electrolyte 14 and the reaction suppression layer 16 is lowered, and the overvoltage in the air electrode 18 is increased, so that the impedance of the cell is increased. The rate of change in impedance temperature is a confirmation of the degree of increase in impedance when the operating temperature is lowered to 600 (° C.). The smaller this value, the degree of characteristic deterioration for 800 (° C.) operation, that is, The temperature dependence of the output is suppressed. The output and the cell impedance itself at the time of low temperature operation of 600 (° C.) are as shown in the second and third stages of Table 1.

  “GDC forming method” indicates a method for forming the reaction suppression layer 16, “printing” is a screen printing method, and “PLD” is a pulse laser deposition method. “GDC relative density” indicates a relative value (%) with respect to the theoretical density of GDC constituting the reaction suppression layer 16.

  The “interface nanoparticle” indicates the presence or absence of the fine particles 20 at the interface between the reaction suppression layer 16 and the air electrode 18, and the average particle size in the “nanoparticle diameter” column for the particles provided with the fine particles 20. The diameter is shown.

  In addition, “heat cycle peeling” repeats operation / stop under the condition that the temperature is raised / lowered at 400 (° C./h) between an operation state of 600 (° C.) and a stop state of 200 (° C.). It was confirmed whether or not peeling occurred between the air electrode 18 and the air electrode 18, and “existing” indicates that peeling occurred until 50 heat cycles, and “no” indicates that peeling did not occur.

According to the above evaluation results, in Comparative Example 1 of the conventional structure, the output of 800 (° C.) is as low as 0.83 (W / cm ² ), and the output of 600 (° C.) is only 23 (%) of 0.19 (W / cm ² ). whereas remained cm ^2), in examples 1 to 5, 800 (° C.) output not only as high as ^{0.98~1.20 (W / cm 2),} 600 (℃) output is also from 0.35 to 0.57 ( W / cm ² ), and an output of 800 (° C.) of about 36 to 48 (%) was obtained. The difference between Example 1 and Comparative Example 1 is only the presence or absence of fine particles 20, which contributes to the improvement of oxygen reduction activity, the reduction of the air electrode overvoltage in low temperature operation, the improvement of ionic conductivity, and the output of SOFC10. It is thought that while improving, the output fall at the time of low-temperature driving | operation was suppressed.

In particular, in Examples 2 to 5 in which the reaction suppression layer 16 was formed by the pulse laser deposition method, the 800 (° C.) output was further improved to 1.02 to 1.20 (W / cm ² ), and the 600 (° C.) output was 0.47 to A remarkable improvement of 46-48 (%) was observed for 0.57 (W / cm ² ) and 800 (° C) output. This is presumably because the reaction suppression layer 16 formed by the pulse laser deposition method has a relative density as high as 98 (%), and the ion conductivity is enhanced.

The effects of the fine particles 20 and the high-density reaction-suppressing layer 16 remarkably appear in “cell impedance 600 ° C.” in Table 1 above. The cell impedance is 2.32 (Ω · cm ² ) in Comparative Example 1, whereas 1.40 (Ω · cm ² ) in Example 1 in which the fine particles 20 are provided, and a high-density reaction suppression layer by pulse laser deposition. In Examples 2 to 5 in which 16 is formed, it is remarkably small as 1.03 to 1.34 (Ω · cm ² ). The reason why the cell impedance is reduced in this way is considered to be due to the presence of the fine particles 20 and the increase in the density of the reaction suppression layer 16, and as a result, the output is improved. The degree of improvement in characteristics when the operating temperature is lowered is also apparent from the “impedance temperature change rate”. The impedance temperature change rate is extremely high at 244 (%) in Comparative Example 1, whereas it remains at 132 to 198 (%) in Examples 1 to 5. In particular, in Examples 2 to 5 using the pulse laser deposition method, the impedance temperature change rate remains at 160 (%) or less. As described above, according to the present embodiment, a decrease in power generation performance is suppressed even when the operation temperature is lowered to 600 (° C.) with respect to the high temperature operation of 800 (° C.) or higher that has been conventionally performed. Yes.

In Comparative Examples 2 and 3, the reaction suppression layer 16 is formed by a pulse laser deposition method. In Comparative Example 2, the fine particles 20 are not formed, and in Comparative Example 3, an LSC film is formed instead of the fine particles 20. As a result, the cell impedance is lower than that of Comparative Example 1 and the output of 600 (° C.) is improved to about 0.30 (W / cm ² ), but the results are inferior to those of Examples 1 to 5. is there.

  Moreover, in Examples 1 to 5 in which the fine particles 20 are provided, any heat cycle peeling does not occur and a practical life is achieved. On the other hand, in Comparative Examples 1 to 3 in which the fine particles 20 are not provided, any peeling occurs up to 10 times, which is not practical. In particular, in Comparative Examples 2 and 3 in which the reaction suppression layer 16 was provided by the pulse laser deposition method, even when compared with Comparative Example 1 having a conventional structure, peeling occurred in a short heat cycle. Since the relative density of the reaction suppression layer 16 is as high as 98 (%), it is considered that the surface smoothness is improved and the bonding force with the air electrode 18 is further reduced.

Further, among Examples 2 to 5, in Examples 3 and 4 in which the particle diameter of the fine particles 20 is 10 to 50 (nm), the ratio of 600 (° C.) output to 800 (° C.) output is the most 48 (%). High results were obtained. Particularly, in Example 3 in which the particle size of the fine particles 20 is 10 (nm), the cell impedance at 600 (° C.) is extremely small as 1.03 (Ω · cm ² ), and the output at 600 (° C.) is 0.57 (W / cm ² ). The highest result was obtained. In Example 2 in which the particle size of the fine particles 20 is 5 (nm), the cell impedance at 600 (° C.) is 1.12 (Ω · cm ² ), and the output at 600 (° C.) is 0.55 (W / cm ² ). This is the second result. A sufficient effect can be obtained even if the average particle size of the fine particles 20 is any of 5 to 100 (nm) evaluated, but a range of 5 to 50 (nm) is particularly preferable, and about 10 (nm) is most preferable. It is considered a thing.

  As described above, according to the present embodiment, since the fine particles 20 made of the same material as the air electrode 18 exist at the interface between the reaction suppression layer 16 and the air electrode 18, not only the output is improved, Since peeling due to heat cycle is suppressed, SOFC 10 suitable for low temperature operation of about 600 (° C.) can be obtained.

  Further, when the reaction suppression layer 16 is formed by the pulse laser deposition method as in Examples 2 to 5, since the relative density is also increased, the cell impedance is further reduced, and the output is 800 (C) and 600 (C) both have the advantage of being improved.

  In the present embodiment, in the SOFC 10, the fine particles 20 are provided on the reaction suppression layer 16 by the pulse laser deposition method in the fine particle formation step P6. According to the pulse laser deposition method, the particle diameter can be easily controlled by changing the number of shots as described above, and the particles can be formed without compositional deviation. Therefore, for example, in the range of 5 to 100 (nm), there is an advantage that the fine particles 20 having the same composition as the air electrode 18 having a desired particle diameter can be easily formed.

  In addition, according to the present example, since the reaction suppression layer 16 is formed by the pulse laser deposition method in the reaction suppression layer forming step P5, the high density of the relative density as high as 98 (%) that cannot be obtained by the printing method. A quality film can be easily obtained. Therefore, as described above, the ion conductivity of the reaction suppression layer 16 is increased, and the power generation performance is improved.

  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 SOFC
12 Fuel electrode 14 Electrolyte 16 Reaction inhibition layer 18 Air electrode 20 Fine particles

Claims (7)

A solid oxide fuel cell in which an electrolyte, a reaction suppression layer, and an air electrode are sequentially laminated on one surface of a fuel electrode,
A solid oxide fuel cell comprising a large number of fine particles having an average particle diameter of 5 to 100 (nm) distributed over the entire interface between the reaction suppression layer and the air electrode.   2. The solid oxide fuel cell according to claim 1, wherein the plurality of fine particles are made of the same material as the air electrode.   The solid oxide fuel cell according to claim 1 or 2, wherein the reaction suppression layer is made of gadolinium-doped ceria (GDC).   The solid oxide fuel cell according to any one of claims 1 to 3, wherein the reaction suppression layer has a relative density of 95 (%) or more.   The solid oxide fuel cell according to any one of claims 1 to 4, wherein the reaction suppression layer is formed by a pulsed laser deposition method.   The solid oxide fuel cell according to any one of claims 1 to 5, wherein the large number of fine particles are formed by a pulsed laser deposition method. The air electrode material is (La _1-x Sr _x ) (Co _1-y Fe _y ) O _3-δ (where 0 <x <1, 0 ≦ y <1, 0 ≦ δ <1). The solid oxide fuel cell according to any one of claims 1 to 6.