JP2020030991A - Solid oxide fuel cell - Google Patents

Abstract

To provide a high-performance solid oxide fuel cell that maintains high electron conductivity required for a current collector layer while improving sulfur poisoning resistance in order to solve a problem of sulfur poisoning of an air electrode layer of a fuel cell by sulfur contained in air for power generation.SOLUTION: In a solid oxide fuel cell in which a fuel electrode layer and an air electrode layer are stacked with a solid oxide electrolyte layer interposed, a current-collecting layer containing silver is provided on the outer surface of the air electrode layer, and the current-collecting layer contains a perovskite-type oxide containing an alkaline earth metal, and the perimeter/area of the gas phase is 5.0 μmor more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a solid oxide fuel cell that generates power by a reaction between a fuel gas obtained by reforming a source gas and an oxidizing gas.

  A solid oxide fuel cell device (Solid Oxide Fuel Cell: hereinafter also referred to as “SOFC”) uses an oxide ion conductive solid electrolyte as an electrolyte and has a plurality of solid oxide fuel cells having electrodes attached to both sides thereof. It is arranged in a module container, and supplies fuel gas to one electrode (fuel electrode) and oxidant gas (air, oxygen, etc.) to one electrode (air electrode) of the solid oxide fuel cell. This is a device that takes out the power generated by the power generation reaction. It operates at a relatively high temperature of, for example, about 600 to 1000 ° C. with respect to other fuel cell devices such as a polymer electrolyte fuel cell device.

Here, in general, the oxidizing gas supplied to the solid oxide fuel cell device contains a sulfur compound such as SO ₂ . It is known that the sulfur compound reacts with the air electrode to reduce the catalytic activity of the air electrode, that is, a problem of sulfur poisoning of the air electrode. Since it is common to use air in the atmosphere as the oxidizing gas, especially in locations where high levels of sulfur compounds such as automobile exhaust gas and sulfur gas are released along arterial roads and hot springs, The deterioration of the cathode will be accelerated. As a countermeasure, it is conceivable to attach a sulfur filter so that a sulfur compound contained in the oxidizing gas does not reach the air electrode in the solid oxide fuel cell device. However, in view of an increase in apparatus price and an increase in maintenance load, it has been required to solve the problem of sulfur poisoning of the air electrode by using a filterless apparatus configuration.

To solve the problem without providing a special sulfur filter, by a three-layer structure of the Patent Document 1 to the air electrode layer electrode reaction layer and the SO _x adsorption layer and the current collecting layer, the SO _x adsorption layer while selectively adsorb sO _x in the air, it is described that can achieve both the ensuring of catalytic activity function and electron conductivity.

JP-A-2006-177987

The SO _x adsorption layer described in Patent Document 1 described above is composed of an oxide containing an alkaline earth metal (Sr) exemplified by La _0.5 Sr _0.5 CoO ₃ . The SO _x adsorbing layer is a separately provided functional layer for selectively adsorbing sulfur compounds in the air by the alkaline earth metal. Therefore, the SO _x adsorbing layer should not be provided unless there is an influence of sulfur poisoning. That is, by additionally inserting an SO _x adsorption layer made of an oxide between the electrode reaction layer and the current collecting layer, a resistance component is added to a conduction path of electrons from the electrode reaction layer to the current collecting layer. The current extraction efficiency is reduced in the cell. Particularly, in a general solid oxide fuel cell device, a voltage that can be output by one fuel cell is limited to about 1 V, and a necessary output is secured by connecting a plurality of these in series. For this reason, since the resistance component generated by the insertion of the SO _x adsorption layer is added in the series circuit, in a cell stack in which a plurality of solid oxide fuel cells are electrically connected, the resistance component is increased. The reduction in current extraction efficiency becomes significant.

  In order to solve the problem of sulfur poisoning of the air electrode layer of the solid oxide fuel cell by the sulfur contained in the air for power generation, the present invention improves the sulfur poisoning resistance while improving the sulfur poisoning resistance. An object of the present invention is to provide a high-performance solid oxide fuel cell maintaining high required electron conductivity.

  The inventor of the present invention has conceived that by adjusting the particle diameter of the raw material and the amount of the perovskite-type oxide added, it is possible to achieve both the conductive performance and the sulfur collecting performance in the current collecting layer while securing air permeability.

That is, one embodiment of the solid oxide fuel cell according to the present invention is a solid oxide fuel cell in which a fuel electrode layer and an air electrode layer are stacked with a solid oxide electrolyte layer interposed therebetween. Having a current collecting layer on the outer surface of the air electrode layer, the current collecting layer containing a perovskite oxide containing an alkaline earth metal, and having a perimeter / area of the gas phase of 5.0 μm ⁻¹ or more. It is.

According to this aspect, it is possible to add a sulfur compound collection function while maintaining current collection performance without lowering the current extraction efficiency of the solid oxide fuel cell and ensuring air permeability. it can. Therefore, it is possible to provide a solid oxide fuel cell having high durability without deterioration in performance. When the perimeter / area of the gas phase is less than 5.0 μm ⁻¹ , the probability of occurrence of a short path reaching the air electrode without adsorbing and removing sulfur contained in the air increases, and as a result, the air electrode and sulfur The reaction causes a reduction in the catalytic activity of the air electrode.

  Note that the solid oxide fuel cell described in this specification includes a fuel electrode layer, an electrolyte layer, an air electrode layer, and a current collecting layer, but does not exclude other configurations, for example, an electrolyte layer and an air electrode. A reaction preventing layer for preventing a reaction between constituent materials may be provided between the layer and the layer.

  In one embodiment of the present invention, the current collecting layer preferably includes only one layer.

For example, the SO _x adsorption layer is formed of a layer containing a large amount of LSCF (LSCF having a thermal expansion of 15.4 × 10 ⁻⁶ / ° C.), and the current collecting layer is formed of a layer containing a large amount of Ag (Ag having a thermal expansion coefficient of 24 ×). When formed at a temperature of 10 ⁻⁶ / ° C.), a large stress is generated at the interface due to a difference in thermal expansion, so that peeling is likely to occur. With one layer, reliability can be increased.

  In one embodiment of the present invention, the porosity of the current collecting layer is preferably 40% or less.

  If the porosity becomes too large, the probability of occurrence of a short path reaching the air electrode without adsorbing and removing sulfur contained in the air increases, and as a result, the air electrode reacts with sulfur to increase the catalytic activity of the air electrode. Will drop. By setting the porosity of the current collecting layer to 40% or less, occurrence of a short path can be suppressed. Also, more preferably, the porosity of the current collecting layer is 33% or less, whereby high conductivity can be obtained.

  In order to solve the problem of sulfur poisoning of the air electrode layer of the solid oxide fuel cell by the sulfur contained in the air for power generation, a sulfur collection function was provided in the current collector layer provided above the air electrode layer. In addition, it is possible to provide a highly durable solid oxide fuel cell unit that secures the original conduction function of the current collecting layer.

FIG. 1 is a schematic diagram showing one embodiment of a cross section of a solid oxide fuel cell unit of the present invention. 1 is an overall configuration diagram showing a solid oxide fuel cell system. FIG. 2 is a side sectional view showing a solid oxide fuel cell module of the solid oxide fuel cell system. FIG. 2 is a perspective view showing a solid oxide fuel cell stack of the solid oxide fuel cell system. FIG. 2 is a partial cross-sectional view showing a solid oxide fuel cell unit of the solid oxide fuel cell system. FIG. 3 is a sectional view taken along line III-III in FIG. 3.

  Hereinafter, embodiments of the invention disclosed in this specification will be described in detail with reference to the drawings. From the following description, many modifications and other embodiments of the present invention are obvious to one skilled in the art. Accordingly, the following description is to be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the invention. Details of its structure and / or function may be substantially changed without departing from the spirit of the invention.

  The shape of the solid oxide fuel cell of the present invention is not limited to a specific shape, and may be, for example, a cylinder, a plate, or a hollow plate having a plurality of gas channels formed therein. Preferably, it is a solid oxide fuel cell having a cylindrical shape.

The solid oxide fuel cell according to the present invention is a solid oxide fuel cell in which a fuel electrode layer and an air electrode layer are laminated with a solid oxide electrolyte layer interposed therebetween, A current collecting layer is provided on the outer surface, and the current collecting layer contains a perovskite-type oxide containing an alkaline earth metal and has a perimeter / area of a gas phase of 5.0 μm ⁻¹ or more.

[Fuel electrode layer]
The fuel electrode layer is, for example, a mixture of Ni and zirconia doped with at least one selected from rare earth elements such as Ca, Y and Sc, and a mixture of Ni and ceria doped with at least one selected from rare earth elements. And a mixture of Ni and lanthanum gallate doped with at least one selected from Sr, Mg, Co, Fe and Cu.

  In the present specification, the fuel electrode layer refers to a fuel electrode catalyst layer that generates hydrogen ions by a metal catalyst such as Ni contained from a supplied hydrogen-containing fuel gas, or a functional layer such as a fuel electrode catalyst layer. It may include a support for lamination. For example, the fuel electrode layer may be a laminate of a conductive support and a fuel electrode catalyst layer formed on the outer surface thereof, or a laminate of the insulating support and the fuel electrode catalyst layer formed on the outer surface thereof. It may be a laminate. When an insulating support is used, a fuel electrode current collecting layer (also simply referred to as a fuel electrode or a fuel electrode side conductive layer) is arranged between the fuel electrode catalyst layer and the fuel electrode catalyst layer. Further, a laminated structure including an intermediate layer, a concentration gradient layer, and the like separately provided for improving the function and durability of the fuel electrode layer may be used.

  Similarly, the electrolyte layer and the air electrode layer may be a laminated structure including an intermediate layer, a concentration gradient layer, and the like separately provided for improving these functions and improving durability.

[Electrolyte layer]
The electrolyte layer is formed over the entire circumference along the outer peripheral surface of the fuel electrode layer, with the lower end terminating above the lower end of the fuel electrode layer and the upper end terminating below the upper end of the fuel electrode layer. . The electrolyte layer is, for example, zirconia doped with at least one selected from rare earth elements such as Y and Sc, ceria doped with at least one selected from rare earth elements, lanthanum gallate doped with at least one selected from Sr and Mg, It is formed from at least one.

The electrolyte layer is preferably Sr and Mg are doped lanthanum gallate-based oxide, more preferably the general formula _{La 1-a Sr a Ga 1} -bc Mg b Co c O 3 ( where 0.05 ≦ a ≦ 0.3, 0 <b <0.3, 0 ≦ c ≦ 0.15) is a lanthanum gallate-based oxide (LSGM). When LSGM is used as an electrolyte layer of a fuel cell used in a solid oxide fuel cell device, a reaction between an air electrode layer and a sulfur compound in a relatively low operating temperature range of 600 ° C. to 700 ° C. which is a characteristic of LSGM. Is particularly remarkable. In one embodiment of the present invention, even when LSGM is used, sulfur poisoning of the air electrode can be sufficiently suppressed, so that high overall energy efficiency can be obtained as a solid oxide fuel cell device. it can. The electrolyte layer may contain components other than the above-described materials as trace components.

[Air electrode layer]
The air electrode layer is formed over the entire circumference along the outer peripheral surface of the electrolyte layer, with the lower end ending above the lower end of the electrolyte layer and the upper end ending below the upper end of the electrolyte layer.

  The air electrode layer preferably contains a perovskite oxide containing the same alkaline earth metal as the alkaline earth metal contained in the current collecting layer. By using the same alkaline earth metal for the current collecting layer and the air electrode layer, it is possible to improve the adhesion between the current collecting layer and the air electrode layer, prevent film peeling, and improve the durability of the fuel cell. Performance can be improved. As the alkaline earth metal, at least one selected from strontium (Sr), calcium (Ca), and barium (Ba) can be used.

The alkaline earth metal contained in the air electrode layer is preferably contained as a perovskite oxide. As perovskite oxides, La _1-x Sr _x CoO ₃ (where x = 0.1-0.3) and LaCo _1-x Ni _x O ₃ (where x = 0.1-0.6) lanthanum cobalt oxides such as, (La, Sr) FeO ₃ system and (La, Sr) CoO ₃ lanthanum cobalt ferrite-based oxide is a solid solution of _{(La 1-m Sr m Co} 1-n Fe n O 3 (However, 0.05 <m <0.50, 0 ≦ n ≦ 1)) and samarium-cobalt-based oxides containing samarium and cobalt (Sm _0.5 Sr _0.5 CoO ₃ ). Preferably, it is lanthanum strontium cobaltite ferrite (LSCF).

  The thickness of the air electrode layer is preferably from 10 μm to 60 μm, more preferably from 10 μm to 45 μm. As a result, an electrode active region is secured, and high performance is obtained. Further, it is possible to prevent interfacial peeling due to shrinkage during firing during production. Further, the adhesion to the underlayer can be increased, and high cell performance can be obtained.

  The fuel electrode layer functions as a (-) electrode through which the fuel gas flows through the above-described internal flow path, and the air electrode comes into contact with air (oxidizing gas) supplied from outside the fuel cell unit 1100 (+) electrode. Function as

[Current collecting layer]
The current collecting layer is formed on the outer surface of the air electrode layer. The current collecting layer has a perovskite oxide containing an alkaline earth metal. The current-collecting layer has a perimeter / area of a gas phase of 5.0 μm ⁻¹ or more, preferably 5.0 μm ⁻¹ or more and 50 μm ⁻¹ or less. The perimeter of the gas phase is the sum of the perimeters of the pores present in the cross section of the current collector film. The area is the total area of the pores used for measuring the perimeter of the cross section of the current collector film. If the perimeter / area is too large, sintering (= sintering) of silver proceeds during operation, and as a result, the connection between silver is broken, the conductivity is reduced, and the power generation performance is reduced.

  In the present invention, the current collecting layer plays a role of conducting electrons accompanying power generation and a role of collecting sulfur compounds. It becomes possible to collect sulfur compounds such as SOx contained in the oxygen-containing gas and prevent them from being supplied to the air electrode layer.

  The current collecting layer preferably contains silver in order to exhibit conductivity. The current collecting layer preferably contains 30 wt% or more of silver, more preferably 60 wt% or more, and even more preferably 70 wt% or more.

  As the alkaline earth metal contained in the current collecting layer, at least one selected from strontium (Sr), calcium (Ca), and barium (Ba) can be used.

The alkaline earth metal contained in the current collecting layer is preferably contained as a perovskite oxide. Perovskite oxides include lanthanum cobalt-based oxides such as La _1-x Sr _x CoO ₃ (x = 0.1 to 0.3), (La, Sr) FeO ₃ -based and (La, Sr) CoO ₃ lanthanum cobalt ferrite-based oxide is a solid solution of _{(La 1-m Sr m Co} 1-n Fe n O 3 ( where, 0.05 <m <0.50,0 ≦ n ≦ 1)), samarium And a samarium-cobalt-based oxide containing cobalt (Sm _0.5 Sr _0.5 CoO ₃ ). Preferably, it is lanthanum strontium cobaltite ferrite (LSCF).

  The concentration of the perovskite oxide contained in the current collecting layer is preferably 1 wt% or more and 70 wt% or less, more preferably 10 wt% or more and 40 wt% or less, and even more preferably 20 wt% or more and 30 wt% or less. preferable. Thereby, it is possible to provide a long-term reliable current collecting layer having both the conductive performance and the sulfur collecting performance. That is, it is possible to exhibit the function as a current collecting layer while exhibiting the sulfur collecting ability for a long period of time. Further, when the current collecting layer contains silver, it is possible to prevent the silver sintering during production or operation from excessively progressing, thereby preventing the film from becoming dense and impairing the oxygen permeability.

  In the present invention, the concentration of the alkaline earth metal contained in the current collecting layer can be determined by the following method. The current collecting layer is scraped off from the manufactured solid oxide fuel cell. After dissolving the shaved material with an acid, it can be determined by ICP-emission spectrometry.

  The current collecting layer may include an additive such as a sintering aid. Examples of the additive include palladium (Pd), copper (Cu), bismuth (Bi), and the like. Thereby, the sinterability of silver is improved, and the bonding strength with the air electrode layer can be ensured.

  The thickness of the current collecting layer is preferably from 10 μm to 120 μm, more preferably from 10 μm to 60 μm, even more preferably from 10 μm to 40 μm. When the film thickness is less than 10 μm, the long-term sulfur trapping ability is inferior and the performance is reduced. On the other hand, when the thickness is larger than 120 μm, the diffusion resistance of the air is high, and the air supply to the air electrode catalyst is insufficient, and the performance is reduced. This tendency begins to appear above 60 μm. In addition, although there is no difference in the single power generation performance, when the power generation performance exceeds 40 μm, the performance during operation is reduced. The higher the conductivity of the current collecting layer is, the more preferable it is. However, it is more preferably 1,000 to S / cm 60000 S / cm at 700 ° C., and still more preferably 10,000 to S / cm 40000 S / cm.

  In the present invention, the solid oxide fuel cell may have a cylindrical shape provided with an electrolyte layer, an air electrode layer, and a current collecting layer toward the outside of the fuel electrode layer disposed inside. In this case, the fuel electrode layer has an internal flow path through which the fuel gas flows in the axial direction of the solid oxide fuel cell, and the current collecting layer has a fuel cell in which the fuel gas is supplied to at least the internal flow path. Is preferably provided in the vicinity of one end side of the. Here, in the present specification, the “cylindrical shape” is a fuel cell having a three-dimensional shape extending in one axial direction, and includes a hollow shape having at least one passage penetrating in the axial direction. For example, three-dimensional shapes such as a cylindrical shape and a flat cylindrical shape are included.

  When a cylindrical solid oxide fuel cell is used for a solid oxide fuel cell device, hydrogen in the supplied fuel gas is reduced because the shape of the fuel cell extends uniaxially. In the vicinity of one end, more power is consumed. In order to realize this power generation reaction, an oxidizing gas is supplied from the outside of the fuel cell toward one end. In this way, the power generation reaction at one end is increased in the axial distribution of the solid oxide fuel cell.

As described above, since the power generation reaction is active near one end of the solid oxide fuel cell, when a sulfur component is adsorbed on the air electrode layer, an alkaline earth metal element (for example, an air electrode) in the air electrode layer is removed. Sr) constituting the layer is pulled out to form an oxide (for example, SrSO ₄ ), and sulfur poisoning occurs.

  When the current collecting layer is provided near one end of the cylindrical solid oxide fuel cell, the sulfur poisoning of the air electrode layer can be prevented.

  Furthermore, since the current generated by the power generation reaction flows toward the current collecting terminal of the solid oxide fuel cell, current concentration occurs at one end where the power generation reaction is active. In particular, when a current collecting terminal is installed near this one end, current concentration at one end becomes more remarkable. Under such current concentration, as will be described later, Cr (chromium) evaporating from the metal members constituting the solid oxide fuel cell stack or the solid oxide fuel cell module diffuses in the air electrode layer, Precipitation in the reaction field causes the problem of chromium poisoning, which degrades the cathode layer.

  It was found that the current-collecting layer containing a perovskite-type oxide containing an alkaline earth metal also had a function of collecting Cr. For this reason, the present invention can also exert an effect of suppressing chromium poisoning which becomes remarkable due to current concentration caused by the cylindrical solid oxide fuel cell structure.

  FIG. 1 is a schematic view showing one embodiment of a cross section of a solid oxide fuel cell according to the present invention, and shows a type in which an inner electrode is a fuel electrode layer. The solid oxide fuel cell 210 according to the present invention includes, for example, a porous support 201, a (first / second) fuel electrode layer 202, a (first / second) electrolyte layer 203, and a (first / second) electrolyte layer. 2) It is composed of an air electrode layer 204 and a current collecting layer 205. In the solid oxide fuel cell unit of the present invention, the preferred thickness of each layer is 0.5 to 2 mm for the porous support, 10 to 200 μm for the first fuel electrode layer, 0 to 30 μm for the second fuel electrode layer, The first electrolyte layer is 0 to 20 μm, the second electrolyte layer is 5 to 60 μm, and the air electrode is 10 to 60 μm. Here, the (first / second) means "a single layer or two layers, and in the case of two layers, has a first layer and a second layer".

[Method of Manufacturing Fuel Cell]
The solid oxide fuel cell of the present invention can be appropriately manufactured according to a known method. The preferred production method is as follows.

  The air electrode, the electrolyte layer, and the fuel electrode layer are prepared by adding a forming aid such as a solvent (water, alcohol, etc.), a dispersant, and a binder to each raw material powder to form a slurry, coating the slurry, and drying the slurry. And firing (1100 ° C. or higher and lower than 1400 ° C.).

  The coating can be preferably performed by a slurry coating method of coating a slurry liquid, a tape casting method, a doctor blade method, a transfer method, or the like. A printing method is also available, and a screen printing method, an inkjet method, or the like can be used.

  Firing may be performed each time each electrode and electrolyte layer is formed, but it is also possible to perform "co-firing" in which a plurality of layers are fired at once. In addition, it is preferable that the baking is performed in an oxidizing atmosphere so that the electrolyte layer is not denatured by diffusion of the dopant. More preferably, baking is performed in an atmosphere having an oxygen concentration of 20 mol% or more and 30 mol% or less using a mixed gas of air and oxygen.

  According to a preferred aspect of the present invention, when the fuel electrode layer is used for the inner electrode and the air electrode layer is used for the outer electrode, after co-firing the fuel electrode and the electrolyte layer, the air electrode layer is formed, and the co-firing is performed. Fire at low temperature.

  For the current collecting layer, powders of silver, palladium, and a perovskite-type oxide of an alkaline earth metal are prepared, and an amount that is the same as the final composition of the current collecting unit is weighed. This is a coating liquid mixed and dispersed in a solvent together with the resin. This coating liquid is applied to an air electrode, dried, and fired to form a current collecting layer. The application of the coating liquid to the air electrode can be performed by a slurry coating method, a tape casting method, a doctor blade method, a screen printing method, a spin coating method, a spray method, a flow coating method, a roll coating method, or a combination thereof. . Here, examples of the resin include a urethane resin, an acrylic resin, an epoxy resin, and a phenol resin. Examples of the solvent include ethanol, methanol, α-terpineol, dihydroterpineol, n-methyl-2-pyrrolidone, benzyl alcohol, toluene, acetonitrile, 2-phenoxyethanol, and a mixed solvent thereof. The amount of the coating liquid applied to the air electrode may be appropriately determined in consideration of the final thickness of the current collector. The drying is preferably performed at about 50 to 150 ° C. for 0.5 to 5 hours, and the calcination is preferably performed at about 400 to 800 ° C. for 0.5 to 5 hours.

  The solid oxide fuel cell system 1 using the solid oxide fuel cell of the present invention is not limited to a specific one, and a known material can be used for its production and other materials. FIG. 2 is an overall configuration diagram showing a solid oxide fuel cell system according to one embodiment of the present invention. As shown in FIG. 2, the solid oxide fuel cell system 1 includes a solid oxide fuel cell module 2 and an auxiliary unit 4.

  The solid oxide fuel cell module 2 includes a housing 6, in which a sealed space 8 is formed via a heat insulating material 7. Note that the heat insulating material may not be provided. A solid oxide fuel cell assembly 12 that performs a power generation reaction with a fuel gas and an oxidant (air) is disposed in a power generation chamber 10 below the sealed space 8. The solid oxide fuel cell assembly 12 includes ten solid oxide fuel cell stacks 14 (see FIG. 4), and the solid oxide fuel cell stack 14 has 16 solid oxide fuel cell stacks. It is composed of a physical fuel cell unit 16 (see FIG. 5). Thus, the solid oxide fuel cell assembly 12 has 160 solid oxide fuel cell units 16, and all of the solid oxide fuel cell units 16 are connected in series. I have.

  Above the above-described power generation chamber 10 in the sealed space 8 of the solid oxide fuel cell module 2, a combustion chamber 18 is formed. In the combustion chamber 18, the remaining fuel gas not used for the power generation reaction and the remaining fuel gas are generated. The oxidant (air) burns to generate exhaust gas. Above the combustion chamber 18, a reformer 20 for reforming the fuel gas is disposed, and the reformer 20 is heated to a temperature at which a reforming reaction is possible by the combustion heat of the residual gas. ing. Further, above the reformer 20, an air heat exchanger 22 for heating the air by receiving the heat of the reformer 20 and suppressing a decrease in the temperature of the reformer 20 is arranged.

  Next, the auxiliary unit 4 includes a pure water tank 26 for storing water from a water supply source 24 such as a water supply and purifying the pure water with a filter, and a water for adjusting the flow rate of the water supplied from the pure water tank. A flow control unit 28 is provided. The auxiliary unit 4 includes a gas shutoff valve 32 for shutting off fuel gas supplied from a fuel supply source 30 such as city gas, a desulfurizer 36 for removing sulfur from the fuel gas, and a flow rate of the fuel gas. A fuel flow adjustment unit 38 for adjustment is provided. Further, the auxiliary unit 4 includes an electromagnetic valve 42 for shutting off air as an oxidant supplied from an air supply source 40, a reforming air flow rate adjusting unit 44 for adjusting the flow rate of air, and an air flow rate adjusting unit for power generation. 45, a first heater 46 for heating the reforming air supplied to the reformer 20, and a second heater 48 for heating the power generating air supplied to the power generation chamber. The first heater 46 and the second heater 48 are provided for efficiently raising the temperature at the time of startup, but may be omitted.

  Next, the solid oxide fuel cell module 2 is connected to a hot water production device 50 to which exhaust gas is supplied. Tap water is supplied to the hot water production device 50 from the water supply source 24, and the tap water becomes hot water by the heat of the exhaust gas and is supplied to a hot water storage tank of an external water heater (not shown). The solid oxide fuel cell module 2 is provided with a control box 52 for controlling the supply amount of fuel gas and the like. Further, the solid oxide fuel cell module 2 is connected to an inverter 54 which is a power take-out unit (power conversion unit) for supplying power generated by the solid oxide fuel cell module to the outside.

  Next, the internal structure of the solid oxide fuel cell module of the solid oxide fuel cell system will be described with reference to FIGS. FIG. 3 is a side sectional view showing a solid oxide fuel cell module of the solid oxide fuel cell system, and FIG. 6 is a sectional view taken along line III-III of FIG. As shown in FIGS. 3 and 6, in the sealed space 8 in the housing 6 of the solid oxide fuel cell module 2, as described above, the solid oxide fuel cell assembly 12, The porcelain container 20 and the air heat exchanger 22 are arranged.

  The reformer 20 has a pure water introduction pipe 60 for introducing pure water at an upstream end thereof and a reformed gas introduction pipe for introducing a solid oxide fuel gas to be reformed and reforming air. An evaporator 20a and a reformer 20b are formed inside the reformer 20 in this order from the upstream side, and the reformer 20b is filled with a reforming catalyst. The fuel gas and the air mixed with the steam introduced into the reformer 20 are reformed by the reforming catalyst filled in the reformer 20.

  A fuel gas supply pipe 64 is connected to the downstream end of the reformer 20. The fuel gas supply pipe 64 extends downward and is formed below the solid oxide fuel cell assembly 12. And extends horizontally within the manifold 66. A plurality of fuel supply holes 64b are formed in a lower surface of the horizontal portion 64a of the fuel gas supply pipe 64, and the reformed fuel gas is supplied into the manifold 66 from the fuel supply holes 64b.

  Above the manifold 66, a lower support plate 68 having a through hole for supporting the above-described solid oxide fuel cell stack 14 is attached. It is supplied into the fuel cell unit 16.

  Next, an air heat exchanger 22 is provided above the reformer 20. The air heat exchanger 22 includes an air collecting chamber 70 on the upstream side and two air distribution chambers 72 on the downstream side. The air collecting chamber 70 and the air distribution chamber 72 are provided with six air flow pipes 74. Connected by Here, as shown in FIG. 6, the three air flow path tubes 74 form a set (74a, 74b, 74c, 74d, 74e, 74f), and the air in the air collecting chamber 70 is Air flows into the respective air distribution chambers 72 from the air flow pipes 74.

  The air flowing through the six air flow pipes 74 of the air heat exchanger 22 is preheated by the exhaust gas that burns in the combustion chamber 18 and rises. An air introduction pipe 76 is connected to each of the air distribution chambers 72. The air introduction pipe 76 extends downward, and its lower end communicates with the space below the power generation chamber 10 so that the air preheated to the power generation chamber 10 is cooled. Is introduced.

  Next, an exhaust gas chamber 78 is formed below the manifold 66. As shown in FIG. 6, an exhaust gas passage 80 extending vertically is formed inside the front surface 6a and the rear surface 6b, which are surfaces along the longitudinal direction of the housing 6, and the upper end of the exhaust gas passage 80 Communicates with the space in which the air heat exchanger 22 is disposed, and the lower end side communicates with the exhaust gas chamber 78. Further, an exhaust gas exhaust pipe 82 is connected to substantially the center of the lower surface of the exhaust gas chamber 78, and a downstream end of the exhaust gas exhaust pipe 82 is connected to the above-described hot water production device 50 shown in FIG. As shown in FIG. 3, an ignition device 83 for starting the combustion of the fuel gas and the air is provided in the combustion chamber 18.

  Next, the solid oxide fuel cell stack 14 will be described with reference to FIG. FIG. 4 is a perspective view showing a solid oxide fuel cell stack of the solid oxide fuel cell system. As shown in FIG. 4, the solid oxide fuel cell stack 14 includes 16 solid oxide fuel cell units 16, and the lower and upper ends of these solid oxide fuel cell units 16 Are supported by a lower support plate 68 and an upper support plate 100 made of solid oxide ceramic, respectively. The lower support plate 68 and the upper support plate 100 have through holes 68a and 100a, respectively, through which the inner electrode terminals 86 can pass.

  Further, a current collector 102 and an external terminal 104 are attached to the solid oxide fuel cell unit 16. The current collector 102 is electrically connected to the fuel electrode connecting portion 102a electrically connected to the inner electrode terminal 86 attached to the inner electrode 90 serving as the fuel electrode, and to the entire outer peripheral surface of the outer electrode 92 serving as the air electrode. It is integrally formed with the air electrode connecting portion 102b that is connected to the air electrode. The air electrode connecting portion 102b is formed of a vertical portion 102c extending vertically on the surface of the outer electrode 92, and a number of horizontal portions 102d extending horizontally from the vertical portion 102c along the surface of the outer electrode 92. I have. Further, the fuel electrode connecting portion 102a is directed obliquely upward or obliquely downward from the vertical portion 102c of the air electrode connecting portion 102b toward the inner electrode terminal 86 located in the vertical direction of the solid oxide fuel cell unit 16. And extend linearly.

  Furthermore, the inner electrodes at the upper end and the lower end of the two solid oxide fuel cell units 16 located at the ends of the solid oxide fuel cell stack 14 (the left and rear sides in FIG. 4). External terminals 104 are connected to the terminals 86, respectively. These external terminals 104 are connected to external terminals 104 (not shown) of the solid oxide fuel cell unit 16 at the end of the adjacent solid oxide fuel cell stack 14, and as described above, are connected to 160. All of the solid oxide fuel cell units 16 are connected in series.

  Next, the solid oxide fuel cell unit 16 will be described with reference to FIG. FIG. 5 is a partial cross-sectional view showing a solid oxide fuel cell unit of the solid oxide fuel cell system. As shown in FIG. 5, the solid oxide fuel cell unit 16 includes a solid oxide fuel cell 84 and inner electrode terminals respectively connected to upper and lower ends of the solid oxide fuel cell 84. 86. The solid oxide fuel cell 84 is a tubular structure extending vertically, and has an inner electrode 90, an outer electrode 92 on a cylindrical porous support 91 forming a fuel gas flow path 88 therein, An electrolyte layer 94 is provided between the inner electrode 90 and the outer electrode 92.

  Since the inner electrode terminals 86 attached to the upper and lower ends of the solid oxide fuel cell 84 have the same structure, the inner electrode terminals 86 attached to the upper end will be specifically described here. The upper portion 90a of the inner electrode 90 has an outer peripheral surface 90b and an upper end surface 90c exposed to the electrolyte layer 94 and the outer electrode 92. The inner electrode terminal 86 is connected to the outer peripheral surface 90 b of the inner electrode 90 via a conductive sealing material 96, and further, is in direct contact with the upper end surface 90 c of the inner electrode 90, thereby electrically connecting to the inner electrode 90. It is connected. A fuel gas passage 98 communicating with the fuel gas passage 88 of the inner electrode 90 is formed at the center of the inner electrode terminal 86. The solid oxide fuel cell of the present invention is used as the solid oxide fuel cell 84.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

(Examples 1 and 2, and Comparative Examples 1 and 2)
[Preparation of solid oxide fuel cell]
NiO powder and 10 YSZ (10 mol% Y ₂ O ₃ -90 mol% ZrO ₂ ) powder were mixed at a weight ratio of 65:35, and the mixture was subjected to shearing by an extruder and formed into a cylindrical shape while forming primary particles. A burning electrode support was prepared. An anode catalyst layer for accelerating the reaction of the anode was formed on the anode support. The fuel electrode catalyst layer was formed by mixing a mixture of NiO and GDC10 (10 mol% GdO _1.5 -90 mol% CeO ₂ ) at a weight ratio of 50:50 on a fuel electrode support by a slurry coating method. Further, LSGM having a composition of LDC40 (40 mol% LaO _1.5 -60 mol% CeO ₂ ) and La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ is sequentially laminated on the fuel electrode reaction catalyst layer by a slurry coating method to form an electrolyte layer. To obtain a molded product. The obtained molded body was fired at 1300 ° C. Thereafter, a film for the air electrode layer was formed by a slurry coating method, and fired at 1050 ° C. to form an air electrode layer. The air electrode layer slurry was prepared by mixing and pulverizing a raw material powder (LSCF powder) of (La _0.6 Sr _0.4 ) (Co _0.2 Fe _0.8 ) O ₃ , a solvent, and a binder.

  Next, a current collecting layer was formed on the outer surface of the air electrode layer. The coating liquid for forming the current collecting layer was a mixture of silver powder, palladium powder, LSCF powder, a solvent, and a binder. Silver and palladium were in a weight ratio of 90: 1. The weight ratio between the silver-palladium mixed powder and the LSCF was 100-X: X. The particle size (D50) of the silver powder and the weight ratio (X) of the LSCF powder are shown in Table 1. The particle size (D50) of the palladium powder was 0.7 μm, and the particle size (D50) of the LSCF powder was 0.3 μm. The particle diameters of the silver, palladium and LSCF powders were measured by a laser diffraction particle size analyzer. This coating solution was applied to the outer surface of the air electrode layer by an inkjet method, dried at 150 ° C. in a drier, cooled at room temperature, and baked at 700 ° C. for 1 hour. Thus, a current collecting layer was formed on the outer surface of the air electrode layer.

The manufactured solid oxide fuel cell was as shown below. The fuel electrode support had an outer diameter of 10 mm and a wall thickness of 1 mm. The thickness of the fuel electrode reaction catalyst layer was 20 μm. The thickness of the LDC layer was 5 μm. The thickness of the LSGM layer was 30 μm. The thickness of the air electrode layer was 20 μm, and the area of the air electrode was 35 cm ² . The thickness of the current collecting layer was 30 μm.

[Measurement of conductivity of current collecting layer]
The electrical conductivity of the current collecting layer was determined by collecting a value measured by a DC four-terminal method at 700 ° C. in an atmospheric furnace by winding an Ag wire around the manufactured solid oxide fuel cell so as to have a potential line interval of 35 mm. It was calculated using the electromembrane cross-sectional area.

[Measurement of porosity of current collecting layer]
The porosity of the current collecting layer was obtained by analyzing an image obtained when measuring the perimeter / area.

[Preparation of solid oxide fuel cell stack]
A solid oxide fuel cell stack was manufactured by the following method using the manufactured solid oxide fuel cells of Examples and Comparative Examples.

  First, a conductive sealing material having both a current collector and a gas seal is attached to both ends of a porous support also serving as a fuel electrode, and furthermore, a conductive sealing material is covered on both ends of the porous support. Was provided with an inner electrode terminal to produce a solid oxide fuel cell unit. The inner electrode terminal has a diameter smaller than the inner diameter of the porous support serving also as a fuel electrode serving as a fuel gas flow path, and extends from each end of the solid oxide fuel cell to the outside of the solid oxide fuel cell. It has a reduced diameter portion that extends. The solid oxide fuel cell unit was made up of a set of 16 solid oxide fuel cell units, and 16 were connected in series by a connector for connecting the fuel electrode and the air electrode to produce a solid oxide fuel cell stack.

[Durability test on solid oxide fuel cell stack]
An endurance test was performed using the manufactured solid oxide fuel cell stack. A hydrogen-nitrogen mixed gas was used as the fuel gas, and the fuel utilization was set to 75%. Air containing a sulfur dioxide component of 0.5 ppm was supplied as an oxidizing gas by diluting a sulfur dioxide / air mixed gas derived from a gas cylinder with compressor air. This is a sulfur concentration that is about 100 times that of the actual usage environment of the solid oxide fuel cell system. The air utilization rate was set to 40%. The power generation steady temperature was set to 700 ° C., the average current density obtained by dividing the current value by the area of the air electrode was set to 0.2 Acm ⁻² , and continuous operation was performed for about 1000 hours. The time until breakthrough was determined from the voltage change rate. Table 1 shows the results.

[Measurement of perimeter / area of gas phase]
The solid oxide fuel cell is embedded in resin, cut after hardening, and the cut surface is polished (water-resistant abrasive paper # 600 and # 1500) with a hand wrapping machine, and ion milled (Hitachi IM4000PLUS) for 2 hours. Processing was performed to obtain a cross section of the current collecting layer.
Next, an image of the current collecting film was obtained with a secondary electron image obtained by a SEM (SU8202 manufactured by Hitachi) at a magnification of 1500, an acceleration voltage of 12 kV, an emission current of 20 μA, and a condenser lens of 7.
The obtained image was colored by an image processing software (WinROOF 2015) using a binarization process to color pores that appeared black in a secondary electron image, and a measurement item of the perimeter was selected and measured.

REFERENCE SIGNS LIST 1 solid oxide fuel cell system 2 solid oxide fuel cell module 4 auxiliary unit 6 housing 7 heat insulating material 8 sealed space 10 power generation room 12 solid oxide fuel cell assembly 14 solid oxide fuel cell stack 16 Solid oxide fuel cell unit 18 Combustion chamber 20 Reformer 22 Air heat exchanger 24 Water supply source 28 Water flow rate adjustment unit 30 Fuel supply source 32 Gas shutoff valve 36 Desulfurizer 38 Fuel flow rate adjustment unit 40 Air supply Source 42 Solenoid valve 44 Reforming air flow adjustment unit 45 Power generation air flow adjustment unit 46 First heater 48 Second heater 50 Hot water production device 52 Control box 54 Inverter 60 Pure water introduction pipe 62 Reformed gas introduction pipe 64 Fuel Gas supply pipe 66 Manifold 68 Lower support plate 70 Air collecting chamber 72 Air distribution chamber 74 Air flow pipe 76 Empty Air introduction pipe 80 Exhaust gas passage 82 Exhaust gas exhaust pipe 83 Ignition device 84 Fuel cell 86 Inner electrode terminal 88 Fuel gas passage 90 Inner electrode 91 Porous support 92 Outer electrode 94 Electrolyte 100 Upper support plate 102 Current collector

Claims (4)

In a solid oxide fuel cell in which a fuel electrode layer and an air electrode layer are stacked with a solid oxide electrolyte layer interposed therebetween,
Having a current collecting layer on the outer surface of the air electrode layer,
The solid oxide fuel cell according to claim ¹ , wherein the current collecting layer includes a perovskite-type oxide containing an alkaline earth metal, and has a perimeter / area of a gas phase of 5.0 μm ⁻¹ or more.   The solid oxide fuel cell according to claim 1, wherein the current collecting layer includes only one layer.   3. The solid oxide fuel cell according to claim 1, wherein the porosity of the current collecting layer is 40% or less.   4. The solid oxide fuel cell according to claim 1, wherein the current collecting layer is a current collecting layer containing silver.

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