JP7382470B2 - solid oxide fuel cell - Google Patents

Description

The present invention relates to a solid oxide fuel cell capable of preventing separation of an air electrode during shutdown.

One type of fuel cell is a solid oxide fuel cell (SOFC) that uses a solid oxide as a solid electrolyte.

A solid oxide fuel cell using a perovskite oxide such as lanthanum strontium cobaltite ferrite (LSCF) as an air electrode is known. For example, in JP-A No. 2011-44119 (Patent Document 1), in an air electrode material containing a perovskite-type oxide containing lanthanum (La), the total number of moles of elements contained in the A site of the perovskite-type oxide It has been described that particles in the air electrode material have different A/B ratios, where the ratio of the total number of moles of elements contained in the B site of the perovskite oxide is defined as the A/B ratio. ing. It is stated that this provides long-term durability.

Japanese Patent Application Publication No. 2011-44119

We have found that in solid oxide fuel cells, in order to prevent the air electrode from peeling off during shutdown, it is important to keep the Young's modulus of the air electrode within a specific range.

Therefore, an object of the present invention is to provide a solid oxide fuel cell that can suppress separation of the air electrode during shutdown.

The present invention provides a solid oxide fuel cell comprising an air electrode, a fuel electrode, and a solid electrolyte disposed between the air electrode and the fuel electrode, in which the air electrode includes a perovskite oxidized The solid oxide fuel cell is a solid oxide fuel cell including a solid oxide fuel cell having a Young's modulus of 10 GPa or more and less than 50 GPa.

FIG. 1 is a schematic diagram showing one embodiment of a cross section of a solid oxide fuel cell according to the present invention. FIG. 1 is a partial cross-sectional view showing a fuel cell unit according to the present invention. 1 is a configuration diagram showing one embodiment of a solid oxide fuel cell system including a solid oxide fuel cell according to the present invention. 1 is a side sectional view showing a fuel cell module of a solid oxide fuel cell system. FIG. 1 is a perspective view showing a fuel cell stack of a solid oxide fuel cell system. 5 is a sectional view taken along line III-III in FIG. 4. FIG.

Definition The fuel cell according to the present invention is the same as what is normally classified or understood in the art as a solid oxide fuel cell, which comprises at least a fuel electrode, a solid electrolyte, and an air electrode. means. Furthermore, the fuel cell according to the present invention can be used in systems that are understood and will be understood in the future as fuel cell systems in the art. Further, the shape of the fuel cell according to the present invention is not limited, and may be, for example, cylindrical, plate-like, hollow plate-like with a plurality of gas flow channels formed inside, or the like. Further, the inner electrode may be formed on the surface of the support.

Air electrode In the present invention, the air electrode contains a perovskite oxide and has a Young's modulus of 10 GPa or more and less than 50 GPa. This makes it possible to prevent the air electrode from peeling off during shutdown.

The reason for this is considered to be as follows, but the present invention is not limited to this.

The separation of the air electrode during shutdown is thought to be due to the stress applied to the air electrode. As the stress applied to the air electrode, for example, stress added due to reduction expansion when the air electrode is exposed to a reducing atmosphere can be considered.

When the supply of fuel gas and air to the fuel cell is stopped during operation stoppage, especially during shutdown, residual fuel in the fuel piping, reformer, manifold, etc. will be released from the cell opening, which is the outlet of the fuel gas flow path. Gas may blow out and the air electrode may be exposed to a reducing atmosphere. It is known that an air electrode undergoes reduction expansion when exposed to a reducing atmosphere. It is thought that stress due to this reduction and expansion is applied to the air electrode, causing separation of the air electrode during shutdown.

In the air electrode, the relationship between stress σ, Young's modulus E, and strain ε is generally expressed by the following equation (1).
σ=Eε...(1)
When strain ε ₁ due to residual stress during cell firing and strain ε ₂ due to reduction expansion occur on the air electrode, in order to reduce the stress σ applied to the air electrode, the value of Young's modulus E should be designed to be small. is valid. That is, when the Young's modulus of the air electrode is large, necking between particles contained in the air electrode becomes strong, and stress against the strain applied to the air electrode due to shutdown becomes large, so that separation of the air electrode is likely to occur. On the other hand, if the Young's modulus of the air electrode is small, necking between the particles contained in the air electrode is weak, the particles fall off, and the air electrode cannot function as an air electrode.

In the present invention, by setting the Young's modulus of the air electrode to 10 GPa or more and less than 50 GPa, particles contained in the air electrode can neck with each other with appropriate strength. Therefore, the stress applied to the air electrode can be reduced, and separation of the air electrode during shutdown can be prevented.

In the present invention, the Young's modulus of the air electrode can be determined by the following method.

Young's modulus is measured using a nanoindentation method (for example, Elionix ENT-2100). Use a Berkovich type triangular pyramid indenter for the indenter. A Young's modulus of 1140 GPa and a Poisson's ratio of 0.07 can be used for the diamond indenter. The measurement load is set so that the depth of indentation is 1/10 or less of the film thickness of the air electrode. Thereby, the Young's modulus of the air electrode can be determined without being affected by the solid electrolyte formed in the base material of the air electrode. To set the measurement load, the indentation depth is measured when the load is arbitrarily changed at five points, and the relationship between each load and each indentation depth is made into a load load curve. From the obtained curve, the load at which the film thickness of the air electrode becomes 1/10 or less is determined. Using this load, a total of 10 arbitrary points on the surface of the air electrode are measured to calculate the Young's modulus, and the average value of the obtained 10 points is taken as the Young's modulus of the air electrode of the present invention.

In the present invention, the Young's modulus of the air electrode is preferably 10 GPa or more and 40 GPa or less, and more preferably 10 GPa or more and 25 GPa or less. This makes it possible to effectively prevent separation of the air electrode during shutdown.

In the present invention, the perovskite oxide contained in the air electrode preferably contains lanthanum (La) at the A site and cobalt (Co) or iron (Fe) at the B site. Specifically, (La _1-x , Sr _x )CoO ₃ (where x=0.1 to 0.3) and La(Co _1-x , Ni _x )O ₃ (where x=0.1) _~ 0.6), lanthanum cobalt ferrite oxides (La _{1 -m} Sr _m ) (Co _1-n, Fe _n )O ₃ (0.05<m<0.50, 0≦n≦1), samarium cobalt oxide containing samarium and cobalt (Sm _0.5 Sr _0.5 CoO ₃ ), etc. It will be done. Preferably, it is lanthanum strontium cobaltite ferrite (La, Sr) (Co, Fe) O ₃ .

In the present invention, the air electrode has a total number of moles of elements contained in the A site of the perovskite oxide (A) and a total number of moles of the elements contained in the B site of the perovskite oxide (B). When the ratio is expressed as an A/B ratio, the A/B ratio of the air electrode is preferably 1.000<A/B ratio≦1.030. In the present invention, for example, a perovskite oxide (ABO ₃ ) having an A/B ratio of 1.001 can be expressed as A _1.001 BO ₃ . This makes it possible to obtain a solid oxide fuel cell that can prevent separation of the air electrode during shutdown and exhibit good power generation performance.

In the present invention, it is further preferable that the air electrode has a ratio of 1.005≦A/B≦1.015. This makes it possible to obtain a solid oxide fuel cell that can prevent separation of the air electrode during shutdown and exhibit good power generation performance.

In the present invention, the number of moles of the element contained in the A site (A) and the number of moles of the element contained in the B site (B) of the perovskite oxide contained in the air electrode are determined by the following method.

Method for calculating A/B ratio of perovskite oxide contained in air electrode Prepare oxides of each element constituting perovskite oxide contained in air electrode, mold by glass bead method, and form standard Prepare the sample. Next, the peak intensity of characteristic X-rays of this standard sample is measured using an X-ray fluorescence analyzer (XRF). Thereafter, a calibration curve is created from the composition amount of the standard sample calculated from the weighed values of these standard samples and the peak intensity of the obtained characteristic X-rays.

The produced air electrode is shaved with a commercially available cutter, and the scraped measurement sample is molded using a powder press method to produce an evaluation sample. When scraping the air electrode, it is preferable to scrape off the exposed part of the air electrode, but if a film different from the air electrode is formed on the surface of the air electrode, scraping off this film etc. After removing and exposing the air electrode, it is preferable to shave the air electrode. The peak intensity of characteristic X-rays of this evaluation sample is measured by XRF. The amount (wt%) of each element in the perovskite oxide contained in the air electrode material is determined from the peak intensity of the characteristic X-rays obtained and the above calibration curve. From these, the number of moles of the element contained in the A site (A) and the number of moles of the element contained in the B site (B) of the perovskite oxide are determined.

In the present invention, the air electrode preferably contains elemental sulfur. Specifically, the air electrode preferably contains 4000 ppm or less of sulfur element, and more preferably 1000 ppm or less. Moreover, it is preferable to contain 20 ppm or more, and it is more preferable to contain 50 ppm or more. Thereby, peeling during shutdown can be effectively prevented.

In the present invention, the content and location of the sulfur element contained in the air electrode can be clarified using a GD-OES (glow discharge optical emission spectrometer). GD-OES can obtain the amount of sulfur element corresponding to each position in the thickness direction by analyzing the air electrode in the thickness direction.

In the present invention, the sulfur element contained in the air electrode is preferably present in a scattered manner in the air electrode.

The amount of sulfur element contained in the air electrode can be determined by the following method.

The content of the sulfur element contained in the air electrode can be determined by scraping off the entire air electrode from the fuel cell and analyzing the entire amount obtained using a carbon sulfur analyzer (for example, CS844 manufactured by LECO). If a film different from the air electrode is formed on the surface of the air electrode, it is preferable to remove this film by scraping or the like and then scraping off the entire air electrode.

In the present invention, the air electrode is preferably composed of a surface region of the air electrode within 5 μm from the interface with the solid electrolyte, and an internal region of the air electrode that is a region other than the solid electrolyte side region. Note that the surface area of the air electrode can be specified by the following method.

The fuel cell is cut to include the interface between the air electrode and the solid electrolyte. This cut surface is observed using a scanning electron microscope (SEM) so as to include the interface between the air electrode and the solid electrolyte, and a secondary electron image or a backscattered electron image is obtained. In the obtained electron image, the interface between the solid electrolyte and the air electrode is identified from the difference in contrast and porosity. The area within 5 μm from the interface between the solid electrolyte and the air electrode is defined as the surface area of the air electrode. In addition, if there is unevenness at the interface between the solid electrolyte and the air electrode, 10 points of unevenness on the interface are randomly determined, the positional average value is taken as the interface, and the area within 5 μm from this interface is taken as the surface area of the air electrode.

In the present invention, it is preferable that the content of elemental sulfur contained in the surface region of the air electrode is greater than the content of elemental sulfur contained in the internal region of the air electrode. Thereby, the adhesion between the air electrode and the solid electrolyte can be improved. Further, it is possible to prevent the perovskite oxide particles contained in the internal region of the air electrode from being excessively sintered, and it is possible to secure a contact area between the air and the perovskite oxide particles. This makes it possible to prevent separation of the air electrode during shutdown operation and to obtain a fuel cell with high power generation performance.

In the present invention, the content of sulfur element contained in the surface region of the air electrode can be determined by the following method.

The fuel cell is cut at an arbitrary plane so that the interface between the air electrode and the solid electrolyte is included. This cut surface is observed using a scanning electron microscope/energy dispersive X-ray spectroscopy (SEM-EDX, eg, Hitachi SU8220) at a magnification of 5000 times to obtain an image. By enclosing the surface area of the air electrode identified by the above-described method in the image and quantifying the obtained signal intensity, the content of the sulfur element contained in the surface area of the air electrode can be determined.

In the present invention, the content of sulfur element contained in the internal region of the air electrode can be determined by the following method.

In the fuel cell, a portion corresponding to the internal region of the air electrode is scraped off. By analyzing the obtained air electrode powder using a carbon-sulfur analyzer (for example, CS844 manufactured by LECO), the content of the sulfur element contained in the internal region of the air electrode can be determined.

In the present invention, the surface region of the air electrode preferably contains 50 ppm or more of sulfur element, more preferably 300 ppm or more. Moreover, it is preferable to contain 28000 ppm or less, and it is more preferable to contain 9000 ppm or less. Thereby, separation of the air electrode during shutdown can be effectively prevented.

In the present invention, the internal region of the air electrode preferably contains less elemental sulfur than the surface region of the air electrode. Specifically, it is preferable that the sulfur element is contained in an amount of 20 ppm or more, more preferably 400 ppm or more. Moreover, it is preferably 4000 ppm or less, and more preferably 1000 ppm or less. This makes it possible to effectively prevent separation of the air electrode during shutdown.

In the present invention, the sulfur element contained in the air electrode is preferably contained as a strontium sulfate compound. The strontium sulfate compound refers to a compound containing strontium sulfate and constituent elements contained in the air electrode, such as La, Co, and Fe. This makes it possible to effectively prevent separation of the air electrode during shutdown.

In the present invention, the air electrode may be a single layer or a multilayer. As an example of a multi-layer air electrode, for example, (La, Sr) (Co, Fe) O ₃ is provided as an air electrode catalyst layer on a solid electrolyte, and the air electrode is assembled on the outermost layer of the fuel cell. An example is a structure in which a layer containing (La, Sr) (Co _, Fe) O ₃ and a conductive material (such as Ag or Al ₂ O ₃ ) is provided as the conductive layer.

Fuel electrode In the present invention, the fuel electrode is not particularly limited as long as it can constitute a fuel cell together with the air electrode, but examples include NiO/zirconium-containing oxide, NiO/cerium-containing oxide, etc. . Here, NiO/zirconium-containing oxide means a mixture of NiO and zirconium-containing oxide uniformly at a predetermined ratio. Further, NiO/cerium-containing oxide means a mixture of NiO and cerium-containing oxide uniformly at a predetermined ratio. Examples of the zirconium-containing oxide of the NiO/zirconium-containing oxide include zirconium-containing oxides doped with one or more of CaO, Y ₂ O ₃ , and Sc ₂ O ₃ . In addition, the cerium-containing oxide of NiO/cerium-containing oxide has the general formula Ce1-yLnyO2 (where Ln is La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, It is any one type or a combination of two or more of Lu, Sc, and Y, such as 0.05≦y≦0.50). Note that since NiO is reduced to Ni in a fuel atmosphere, the above-mentioned mixtures become Ni/zirconium-containing oxides or Ni/cerium-containing oxides, respectively.

In the present invention, the fuel electrode may be a single layer or a multilayer. Examples of multilayer fuel electrodes include fuel electrodes with a Ni/YSZ (yttria stabilized zirconia) layer on the side facing the support, or Ni/GDC (Gd ₂ O _{3 )} layers on the side facing the solid electrolyte. -CeO ₂ ) layer (which functions as a fuel electrode catalyst layer), and fuel electrodes having both of these layers.

Solid Electrolyte In the present invention, the solid electrolyte is not particularly limited as long as it can constitute a fuel cell together with the air electrode, but for example, it may be a lanthanum gallate oxide, or any of Y, Ca, and Sc as a solid solution species. Examples include stabilized zirconia in which one or more of the following are solid-dissolved. The solid electrolyte is preferably a lanthanum gallate oxide doped with Sr and Mg, and more preferably has the general formula La _1-a Sr _a Ga _1-bc Mg _b Co _c O ₃ (however, 0.05 ≦a≦0.3, 0<b<0.3, 0≦c≦0.15). According to one preferred embodiment of the present invention, a cerium-based oxide (Ce 1-x La x O 2 (Ce _1-x La _x O ₂ (However, 0 .3<x<0.5)) may be provided. The reaction suppression layer is preferably Ce _0.6 La _0.4 O ₂ .

In the present invention, the solid electrolyte preferably includes a solid electrolyte surface region containing Co on the air electrode side surface, and the thickness of this solid electrolyte surface region is preferably 2 μm or less. This makes it possible to prevent the air electrode from peeling off during shutdown.

In the present invention, the solid electrolyte surface region is a region present on the air electrode side surface of the solid electrolyte, and contains cobalt (Co). The thickness of the solid electrolyte surface region can be determined by the following method. Analysis is performed using an electron beam microanalyzer (EPMA) to include the interface between the solid electrolyte and the air electrode, and the interface is identified. When the interface between the solid electrolyte and the air electrode has irregularities, 10 irregularities on the interface are determined at random, and the positional average value is taken as the interface. By performing EPMA line analysis on the solid electrolyte to clarify whether it contains Co or not, and determining the distance from the above-mentioned interface, the thickness of the solid electrolyte surface region can be determined.

In the present invention, the presence of Co contained in the solid electrolyte can be confirmed by EPMA line analysis. Specifically, the interface between the air electrode and the solid electrolyte is photographed using EPMA at a magnification of 5000 times, and a Co line profile is obtained by Co line analysis. In the obtained Co line profile, the average value of the fluctuation width of the Co line profile is determined in the region where Co is below the detection limit, and this is used as the baseline. The average value of the fluctuation width of the Co line profile included in the air electrode is determined, and this is set as the Co amount of 100. The baseline is set to zero Co amount. Based on this baseline and the Co100 position, identify the position until the amount of Co contained in the solid electrolyte becomes 5 or less, find the shortest distance from this position to the interface between the air electrode and the solid electrolyte, and calculate this. Let it be the thickness of the solid electrolyte surface area.

In the present invention, the solid electrolyte surface region preferably contains Co in an amount of 8% by mass or less, more preferably 5% by mass or less. This can prevent the air electrode from peeling off during shutdown.

In the present invention, the solid electrolyte is composed of a solid electrolyte surface region and a solid electrolyte internal region, and the solid electrolyte internal region preferably does not contain Co. This makes it possible to prevent the air electrode from peeling off during shutdown.

In the present invention, the Co contained in the solid electrolyte surface region is preferably Co diffused from the air electrode during fabrication of the solid oxide fuel cell. In the present invention, the air electrode is produced by coating the surface of a solid electrolyte or its precursor with an air electrode slurry and then firing the slurry. At this time, Co contained in the perovskite oxide contained in the air electrode diffuses into the solid electrolyte, and Co is contained in the solid electrolyte surface region. In the present invention, during firing, the diffusion of Co from the air electrode to the solid electrolyte is suppressed to the surface region of the solid electrolyte, that is, the diffusion of Co to the internal region of the solid electrolyte is extremely small. Therefore, separation of the air electrode during shutdown can be prevented.

In the present invention, the solid electrolyte may be a single layer or a multilayer. An example of a case where the solid electrolyte is a multilayer structure includes a structure in which a solid electrolyte and a reaction suppression layer are provided. For example, a structure in which a reaction suppression layer such as LDC (e.g. Ce _0.6 La _0.4 O ₂ ) is provided between the fuel electrode and the solid electrolyte made of LSGM, or a structure in which a reaction suppression layer such as LDC (e.g. Ce 0.6 La 0.4 O 2 ) is provided between the air electrode and the solid electrolyte made of YSZ, An example is a structure in which a reaction suppression layer such as _0.9 Gd _0.1 O ₂ ) is provided.

Fuel cell FIG. 1 is a schematic diagram showing one embodiment of the cross section of the solid oxide fuel cell of the present invention, and shows a type in which the inner electrode is the fuel electrode. The solid oxide fuel cell 210 of the present invention includes, for example, a porous support 201, a (first/second) fuel electrode 202, a (first/second) solid electrolyte 203, and a (first/second) solid electrolyte 203. ) Consists of an air electrode 204 and a current collecting layer 205. Here, (first/second) means "a single layer or two or more layers, and in the case of two layers, it has a first layer and a second layer." In the solid oxide fuel cell 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 fuel electrode, 0 to 30 μm for the fuel electrode catalyst layer, and 0 to 30 μm for the reaction suppression layer. The solid electrolyte has a thickness of 5 to 60 μm, the air electrode catalyst layer has a thickness of 0 to 50 μm, and the air electrode has a thickness of 10 to 200 μm.

FIG. 2 is a partial sectional view showing a fuel cell unit according to the present invention. As shown in the figure, the fuel cell unit 16 includes a fuel cell 84 and inner electrode terminals 86 connected to the vertical ends of the fuel cell 84, respectively. The fuel cell 84 is a tubular structure extending in the vertical direction, and has an inner electrode layer 90, an outer electrode layer 92, and an inner electrode on a cylindrical porous support 91 that forms a fuel gas flow path 88 inside. A solid electrolyte 94 is located between the layer 90 and the outer electrode layer 92.

Since the inner electrode terminals 86 attached to the upper end side and the lower end side of the fuel cell 84 have the same structure, the inner electrode terminal 86 attached to the upper end side will be specifically described here. The upper part 90a of the inner electrode layer 90 includes an outer peripheral surface 90b exposed to the solid electrolyte 94 and the outer electrode layer 92, and an upper end surface 90c. The inner electrode terminal 86 is connected to the outer circumferential surface 90b of the inner electrode layer 90 via a conductive sealing material 96, and is also in direct contact with the upper end surface 90c of the inner electrode layer 90. electrically connected. A fuel gas flow path 98 is formed in the center of the inner electrode terminal 86 and communicates with the fuel gas flow path 88 of the inner electrode layer 90 .

Air electrode material In the present invention, the air electrode material includes the number of moles (A) of an element contained in the _A site of the perovskite oxide, and the number of moles (A) of the element contained in the A site of the perovskite oxide, The ratio to the number of moles (B) of the element contained in the B site of the oxide is the A/B ratio, and the A/B ratio is preferably 1.000<A/B ratio, more preferably 1. .000<A/B ratio≦1.030. This makes it possible to prevent the air electrode from peeling off during shutdown.

In the present invention, the number of moles of the element contained in the A site (A) and the number of moles of the element contained in the B site (B) of the perovskite oxide contained in the air electrode material are determined by the following method.

Method for calculating A/B ratio of perovskite oxide contained in air electrode material Prepare oxides of each element constituting the perovskite oxide contained in air electrode, mold by glass bead method, Prepare a standard sample. Next, the peak intensity of characteristic X-rays of this standard sample is measured using an X-ray fluorescence analyzer (XRF). Thereafter, a calibration curve is created from the composition amount of the standard sample calculated from the weighed values of these standard samples and the peak intensity of the obtained characteristic X-rays.

The produced air electrode material is molded by a powder press method to produce an evaluation sample. The peak intensity of characteristic X-rays of this evaluation sample is measured by XRF. The amount (wt%) of each element in the perovskite oxide contained in the air electrode material is determined from the peak intensity of the characteristic X-rays obtained and the above calibration curve. From these, the number of moles of the element contained in the A site (A) and the number of moles of the element contained in the B site (B) of the perovskite oxide are determined.

In the present invention, the perovskite oxide preferably contains lanthanum (La) at the A site and cobalt (Co) at the B site. Specifically, (La _1-x , Sr _x )CoO ₃ (where x=0.1 to 0.3) and La(Co _1-x , Ni _x )O ₃ (where x=0.1) _~ 0.6), lanthanum cobalt ferrite oxides (La _{1 -m} Sr _m ) (Co _1-n, Fe _n )O ₃ (0.05<m<0.50, 0≦n≦1), samarium cobalt oxide containing samarium and cobalt (Sm _0.5 Sr _0.5 CoO ₃ ), etc. It will be done. Preferably, it is lanthanum strontium cobaltite ferrite (La, Sr) (Co, Fe) O ₃ .

In the present invention, the air electrode material preferably contains sulfur element, preferably 4000 ppm or less, and more preferably 1000 ppm or less. Moreover, it is preferable to contain more than 20 ppm, and it is more preferable to contain more than 50 ppm. Thereby, separation of the air electrode during shutdown can be effectively prevented.

The sulfur element contained in the air electrode material of the present invention may be derived from a sulfur compound that is blended separately from the perovskite oxide, or it may be derived from a sulfur compound contained in the raw material for preparing the perovskite oxide. It may be something. As the sulfur compound, organic sulfur compounds or inorganic sulfur compounds described in JP 2014-135271 can be used. Moreover, strontium sulfate can be used as an inorganic sulfur compound.

In the present invention, it is preferable to use an organic sulfur compound or strontium sulfate. Thereby, the adhesion between the air electrode and the solid electrolyte can be improved. Further, it is possible to prevent the perovskite oxide particles contained in the internal region of the air electrode from being excessively sintered, and it is possible to secure a contact area between the air and the perovskite oxide particles. This makes it possible to prevent separation of the air electrode during shutdown operation and to obtain a fuel cell with high power generation performance.

Method for manufacturing air electrode material In the present invention, the air electrode material can be manufactured as follows.

When using the liquid phase method Water-soluble nitrates of each element contained in the perovskite oxide are dissolved in water at a predetermined ratio so that the perovskite oxide has a desired composition. By adding NH ₄ OH to this to co-precipitate each insoluble salt, and drying and calcining the precipitate, a powder containing a perovskite-type oxide having a desired composition can be obtained.

When using the solid phase method Raw materials for metal oxides of each element contained in the perovskite oxide are weighed and mixed with a solvent so that the perovskite oxide has a desired composition. Thereafter, the solvent is removed, and the resulting powder is fired and pulverized to obtain a powder containing a perovskite oxide having a desired composition.

In the present invention, the A/B ratio of the air electrode material can be controlled by arbitrarily controlling the weighed value of the raw materials in each method.

A perovskite oxide having a desired composition obtained by each method can be used as an air electrode material. Further, if necessary, it may be used as an air electrode material by mixing with a solvent or the like to form a paste or slurry.

Cell Manufacturing Method The solid oxide fuel cell according to the present invention can be manufactured as appropriate according to known methods. A preferred manufacturing method is as follows.

First, in the present invention, the air electrode is prepared by adding forming aids such as a solvent (water, alcohol, etc.), a dispersant, a binder, etc. to a raw material powder containing an air electrode material having a desired composition ratio to prepare a slurry. It can be obtained by coating it on a solid electrolyte or its precursor, drying, and then firing (preferably at 950° C. or higher and lower than 1200° C.). Here, "coating the solid electrolyte or its precursor" means not only directly coating the solid electrolyte or its precursor with the slurry, but also coating the solid electrolyte or its precursor through an intermediate layer such as a catalyst layer. An embodiment in which the precursor is coated is also included. Further, as described later, the precursor refers to a substance or a molded body before firing that becomes a solid electrolyte by firing in an embodiment in which a solid electrolyte and an air electrode are co-fired at the same time.

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. Further, printing methods can also be used, such as screen printing methods and inkjet methods.

The solid electrolyte and fuel electrode are made by adding forming aids such as a solvent (water, alcohol, etc.), a dispersant, and a binder to each raw material powder to create a slurry, coating it, drying it, and then firing it (1100 ℃ or higher and lower than 1400℃). 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. Further, printing methods can also be used, such as screen printing methods and inkjet methods.

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

According to a preferred embodiment of the present invention, when a fuel electrode is used as the inner electrode and an air electrode is used as the outer electrode, the air electrode is formed after co-firing the fuel electrode and the solid electrolyte, and the air electrode is formed at a temperature lower than that of co-firing. Fire. The preferable firing temperature of the air electrode is in the range of 950°C or higher and lower than 1200°C.

Solid oxide fuel cell and fuel cell system using the same According to the present invention, a solid oxide fuel cell system including the solid oxide fuel cell according to the present invention is provided. FIG. 3 is a configuration diagram showing a solid oxide fuel cell system according to an embodiment of the present invention. As shown in FIG. 3, the solid oxide fuel cell system 1 includes a fuel cell module 2 and an auxiliary unit 4. As shown in FIG.

The fuel cell module 2 includes a housing 6 , and a sealed space 8 is formed inside the housing 6 via a heat insulating material 7 . Note that the heat insulating material may not be provided. A fuel cell assembly 12 that performs a power generation reaction using fuel gas and an oxidizer (air) is arranged in a power generation chamber 10 that is a lower portion of the sealed space 8 . This fuel cell assembly 12 includes 10 fuel cell stacks 14 (see FIG. 5), and this fuel cell stack 14 is composed of 16 fuel cell units 16 (see FIG. 2). There is. In this way, the fuel cell assembly 12 has 160 fuel cell units 16, and all of these fuel cell units 16 are connected in series.

A combustion chamber 18 is formed above the above-mentioned power generation chamber 10 in the sealed space 8 of the fuel cell module 2, and in this combustion chamber 18, the remaining fuel gas not used in the power generation reaction and the remaining oxidizer (air ) is combusted and produces exhaust gas. Further, a reformer 20 for reforming the fuel gas is arranged above the combustion chamber 18, and the reformer 20 is heated by the combustion heat of the residual gas to a temperature at which a reforming reaction can occur. ing. Further, above the reformer 20, an air heat exchanger 22 is arranged to receive heat from the reformer 20 to heat the air and suppress a drop in temperature of the reformer 20.

Next, the auxiliary equipment unit 4 includes a pure water tank 26 that stores water from a water supply source 24 such as a tap and uses a filter to make it pure water, and a water flow rate that adjusts the flow rate of water supplied from this water storage tank. An adjustment unit 28 is provided. The auxiliary equipment unit 4 also includes a gas cutoff valve 32 that cuts off fuel gas supplied from a fuel supply source 30 such as city gas, a desulfurizer 36 that removes sulfur from the fuel gas, and a desulfurizer 36 that controls the flow rate of the fuel gas. A fuel flow rate adjustment unit 38 for adjustment is provided. Furthermore, the auxiliary equipment unit 4 includes a solenoid valve 42 that shuts off air as an oxidizing agent supplied from an air supply source 40, a reforming air flow rate adjustment unit 44 that adjusts the flow rate of air, and a power generation air flow rate adjustment unit. 45, a first heater 46 that heats the reforming air supplied to the reformer 20, and a second heater 48 that heats the power generation air supplied to the power generation room. These first heater 46 and second heater 48 are provided to efficiently raise the temperature at startup, but may be omitted.

Next, the fuel cell module 2 is connected to a hot water production device 50 to which exhaust gas is supplied. This hot water production device 50 is supplied with tap water from a water supply source 24, and this tap water is turned into 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). Furthermore, a control box 52 is attached to the fuel cell module 2 for controlling the supply amount of fuel gas and the like. Furthermore, an inverter 54 is connected to the fuel cell module 2, which is a power extraction section (power conversion section) for supplying the electric power generated by the fuel cell module to the outside.

Next, the internal structure of the fuel cell module of the solid oxide fuel cell system will be explained with reference to FIGS. 4 and 6. FIG. 4 is a side cross-sectional view showing a fuel cell module of the solid oxide fuel cell system, and FIG. 6 is a cross-sectional view taken along line III-III in FIG. 4. As shown in FIGS. 4 and 6, the sealed space 8 in the housing 6 of the fuel cell module 2 includes, in order from the bottom, the fuel cell assembly 12, the reformer 20, and the air heat exchanger. A container 22 is arranged.

The reformer 20 has a pure water introduction pipe 60 for introducing pure water and a reformed gas introduction pipe 62 for introducing the fuel gas to be reformed and reforming air at its upstream end. Furthermore, inside the reformer 20, an evaporation section 20a and a reforming section 20b are formed in order from the upstream side, and the reforming section 20b is filled with a reforming catalyst. The fuel gas and air mixed with water vapor introduced into the reformer 20 are reformed by a reforming catalyst filled in the reformer 20.

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

A lower support plate 68 equipped with a through hole for supporting the fuel cell stack 14 described above is attached above the manifold 66, and the fuel gas in the manifold 66 flows into the fuel cell unit 16. Supplied.

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

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, and the air introduction pipe 76 extends downward, and its lower end side communicates with the space below the power generation room 10, so that preheated air can be supplied to the power generation room 10. will be introduced.

Next, an exhaust gas chamber 78 is formed below the manifold 66. Further, as shown in FIG. 6, an exhaust gas passage 80 extending in the vertical direction is formed inside the front surface 6a and rear surface 6b, which are surfaces along the longitudinal direction of the housing 6. communicates with a space in which the air heat exchanger 22 is arranged, and the lower end communicates with an exhaust gas chamber 78. Further, an exhaust gas exhaust pipe 82 is connected to approximately the center of the lower surface of the exhaust gas chamber 78, and the downstream end of this exhaust gas exhaust pipe 82 is connected to the above-described hot water production device 50 shown in FIG. 3. As shown in FIG. 4, an ignition device 83 for starting combustion of the fuel gas and air is provided in the combustion chamber 18.

Next, the fuel cell stack 14 will be explained with reference to FIG. FIG. 5 is a perspective view showing a fuel cell stack of the solid oxide fuel cell system. As shown in FIG. 5, the fuel cell stack 14 includes 16 fuel cell units 16, and the lower end side and the upper end side of these fuel cell units 16 are respectively connected to a lower ceramic support plate 68 and an upper ceramic support plate 68. It is supported by a support plate 100. Through holes 68a and 100a are formed in the lower support plate 68 and the upper support plate 100, respectively, through which the inner electrode terminals 86 can pass.

Further, a current collector 102 and an external terminal 104 are attached to the fuel cell unit 16. This current collector 102 includes a fuel electrode connecting portion 102a that is electrically connected to an inner electrode terminal 86 attached to an inner electrode layer 90 that is a fuel electrode, and the entire outer peripheral surface of an outer electrode layer 92 that is an air electrode. and an air electrode connecting portion 102b that is electrically connected. The air electrode connecting portion 102b is formed from a vertical portion 102c extending vertically on the surface of the outer electrode layer 92, and a number of horizontal portions 102d extending horizontally from the vertical portion 102c along the surface of the outer electrode layer 92. has been done. Further, the fuel electrode connecting portion 102a extends diagonally upward or diagonally 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 fuel cell unit 16. It is extending.

Furthermore, the inner electrode terminals 86 at the upper and lower ends of the two fuel cell units 16 located at the ends of the fuel cell stack 14 (in the back and front sides of the left end in FIG. 5) are provided with external terminals, respectively. 104 is connected. These external terminals 104 are connected to the external terminals 104 (not shown) of the fuel cell units 16 at the ends of the adjacent fuel cell stacks 14, and as described above, the external terminals 104 of the 160 fuel cell units 16 are connected to each other. Everything is connected in series.

Next, the startup mode of the fuel cell system shown in the figure will be explained. First, the reforming air flow rate adjustment unit 44, the solenoid valve 42, and the mixing section 47 are controlled to increase the amount of reforming air, and air is supplied to the reformer 20. Furthermore, air for power generation is supplied to the power generation room 10 from an air introduction pipe 76 by controlling the power generation air flow rate adjustment unit 45 and the electromagnetic valve 42 . Then, it also controls the fuel flow rate adjustment unit 38 and the mixing unit 47 to increase the supply of fuel gas, supplies the reformed gas to the reformer 20, and the reformed gas sent to the reformer 20. The reforming air is sent into each fuel cell unit 16 from each through hole 69 via the reformer 20, the fuel gas supply pipe 64, and the gas manifold 66. The gas to be reformed and the reforming air sent into each fuel cell unit 16 pass through the fuel gas flow path 88 from the fuel gas flow path 98 formed at the lower end of each fuel cell unit 16, Each of the fuel gases flows out from a fuel gas flow path 98 formed at the upper end. Thereafter, the ignition device 83 ignites the reformed gas flowing out from the upper end of the fuel gas flow path 98 to perform a combustion operation. As a result, the gas to be reformed is combusted within the combustion chamber 18, and a partial oxidation reforming reaction occurs.

Thereafter, on condition that the temperature of the reformer 20 becomes about 600° C. or higher and the temperature of the fuel cell assembly 12 exceeds about 250° C., the autothermal reforming reaction is started. At this time, the water flow rate adjustment unit 28, the fuel flow rate adjustment unit 38, and the reforming air flow rate adjustment unit 44 supply the reformer 20 with a gas in which the gas to be reformed, reforming air, and steam are mixed in advance. . Next, on condition that the temperature of the reformer 20 becomes 650° C. or higher and the temperature of the fuel cell assembly 12 exceeds about 600° C., the steam reforming reaction is started.

As described above, by switching the reforming process in accordance with the progress of the combustion process from ignition, the temperature in the power generating chamber 10 gradually increases. When the temperature of the power generation chamber 10 reaches a predetermined power generation temperature lower than the rated temperature (approximately 700° C.) at which the fuel cell module 2 operates stably, the electric circuit including the fuel cell module 2 is closed. Thereby, the fuel cell module 2 starts generating electricity, current flows through the circuit, and power can be supplied to the outside.

Next, a description will be given of shutdown of the solid oxide fuel cell system according to this embodiment. When the fuel cell system is stopped, the fuel cell stack is cooled by sending a large amount of cooling air while continuing to supply fuel even after the extraction of power from the fuel cell module is stopped. Next, the supply of fuel is stopped when the temperature of the cell stack falls below the oxidation temperature of the fuel electrode of the fuel cell, and from then on, only air for cooling is continued to be supplied until the temperature is sufficiently reduced. The fuel cell can be completely stopped.

Furthermore, in an emergency, the fuel cell system can be stopped by shutting down, which cuts off the power extraction and the supply of fuel gas, air, and water for fuel reformation almost simultaneously. Further, even after stopping the extraction of electric power, it is possible to stop the engine while gradually reducing the fuel, or to stop the engine without flowing purge gas such as N ₂ gas.

"Shut down and stop almost simultaneously" means that the current, air, gas, and water all stop within a very short time of several tens of seconds. For example, the current, air, gas, and water may all be stopped almost simultaneously, or the supply of air and fuel gas may be stopped 10-odd seconds after the current is stopped, and the water supply may be stopped 10-odd seconds later.

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

Example 1
Preparation of slurry for air electrode The slurry for air electrode is a perovskite-type oxide represented by ABO ₃ in air electrode material containing (La _0.6 Sr _0.4 )(Co _0.2 Fe _0.8 )O ₃ . A raw material powder in which the ratio of the number of moles of the element contained in the A site (A) to the number of moles of the element contained in the B site of the perovskite oxide (B) is 1.001, a solvent, and a binder. It was prepared by mixing and pulverizing.

Preparation of solid oxide fuel cell NiO powder and 8YSZ (8 mol% Y ₂ O ₃ -92 mol% ZrO ₂ ) powder were mixed at a weight ratio of 60:40 and sheared with an extruder to form primary particles. The mixture was molded into a cylindrical shape while being allowed to heat up, and calcined at 900°C to produce a combustion electrode support. A fuel electrode catalyst layer was formed on this fuel electrode support to promote the reaction of the fuel electrode. The fuel electrode catalyst layer was formed by forming a film of a mixture of NiO and GDC10 (10 mol% Gd ₂ O ₃ -90 mol% CeO ₂ ) at a weight ratio of 50:50 on the fuel electrode support by a slurry coating method. . Furthermore, LSGM having a composition of LDC40 (40 mol% La ₂ O ₃ -60 mol% CeO ₂ ) and La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ was sequentially laminated on the fuel electrode reaction catalyst layer by a slurry coating method to form a solid electrolyte layer. A molded body was obtained. The obtained molded body was fired at 1300°C. Thereafter, the air electrode slurry was formed into a film by a slurry coating method and fired at 1050° C. to produce a solid oxide fuel cell.

Appearance inspection The appearance of the obtained solid oxide fuel cell was inspected using a stereomicroscope to confirm the presence or absence of cracks on the air electrode surface. At a magnification of 100 times, confirm a total of 3 locations in the fuel cell, 2 locations at both ends in the long axis direction and 1 location at the center. If a crack is confirmed at even 1 location, it will be evaluated as ×, otherwise it will be evaluated as ○. It was evaluated as follows. The results are shown in Table 1.
○: No crack ×: With crack

Analysis of the sulfur element content in the air electrode The sulfur element content in the air electrode was determined by scraping off the air electrode of the fabricated solid oxide fuel cell until the solid electrolyte surface was visible. All of the powder was analyzed using a carbon sulfur analyzer (CS844 manufactured by LECO) to obtain the content of sulfur element contained in the air electrode. The results are shown in Table 1.

Analysis of the A/B ratio of the perovskite oxide contained in the air electrode The A/B ratio of the perovskite oxide contained in the air electrode was determined by scraping off the air electrode of the fabricated solid oxide fuel cell. All of the obtained air electrode powder was analyzed by XRF to obtain the peak intensity of characteristic X-rays. Next, a calibration curve for the air electrode was created using the following method. Oxides of each element constituting the perovskite oxide contained in the air electrode were prepared and molded using the glass bead method to produce a standard sample. Next, the peak intensity of characteristic X-rays of this standard sample was measured using an X-ray fluorescence analyzer (XRF). Thereafter, a calibration curve was created from the composition amounts of the standard samples calculated from the weighed values of these standard samples and the peak intensity of the obtained characteristic X-rays. The amount (wt%) of each element in the perovskite oxide contained in the air electrode was determined from the peak intensity of characteristic X-rays obtained from the air electrode of the solid oxide fuel cell and the above calibration curve. From these, calculate the number of moles of the element contained in the A site of the perovskite oxide (A) and the number of moles of the element contained in the B site (B), and calculate the A/B of the perovskite oxide contained in the air electrode. I got the ratio. The A/B ratio of the perovskite oxide contained in the air electrode was the same as that of the raw material powder. The results are shown in Table 1.

Measurement of Young's Modulus of Air Electrode Young's modulus of the air electrode was measured using the nanoindentation method (Elionix ENT-2100). A Berkovich type triangular pyramid indenter was used as the indenter. The Young's modulus of the diamond indenter was 1140 GPa, and the Poisson's ratio was 0.07. The measurement load was set so that the depth of indentation was 1/10 or less of the film thickness of the air electrode. To set the measurement load, measure the indentation depth when the load is arbitrarily changed at 5 points, create a load load curve based on the relationship between each load and each indentation depth, and use the obtained curve to calculate the film thickness of the air electrode. The load at which the load becomes 1/10 or less was determined. The Young's modulus was calculated by measuring arbitrary 10 points on the surface of the air electrode using this load, and the average value of the obtained 10 points was taken as the Young's modulus of the air electrode of the present invention. The results are shown in Table 1.

The produced 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 10 μm. The thickness of the LDC layer was 5 μm. The thickness of the LSGM layer was 40 μm. The thickness of the air electrode was 20 μm, and the area of the air electrode was 35 cm ² .

Next, a coating liquid was applied onto the air electrode to form an air electrode current collecting layer. The composition of the coating liquid was a mixture of silver powder, palladium powder, LSCF powder, solvent, and binder. This coating liquid was applied to the solid oxide fuel cell by spraying, dried in a dryer, cooled at room temperature, and baked at 700°C for 1 hour to collect the air electrode current on the outside of the air electrode. formed a layer. The air electrode current collecting layer includes silver, palladium, and LSCF.

Power generation test of solid oxide fuel cell A power generation test was conducted using the obtained solid oxide fuel cell (electrode effective area: 35.0 cm ² ). Current collection at the fuel electrode was performed by wrapping an Ag wire around the inner electrode terminal. Current collection at the air electrode was also carried out by wrapping an Ag wire around the outer periphery of the air electrode current collection layer. The power generation conditions were as follows. That is, the fuel gas was a mixed gas of fuel (H ₂ +3%H ₂ O) and N ₂ and the fuel utilization rate was 75%. In addition, air was used as the oxidizing gas. The measurement temperature was 700°C, and the generated potential was measured at a current density of 0.2A/cm ² . The initial performance of the cell was as shown in Table 1 as the initial potential.

Fabrication of solid oxide fuel cell module A conductive sealing material that serves as a current collector and a gas seal is attached to both ends of the fuel electrode support, and a conductive sealing material is attached to both ends of the fuel electrode to cover the conductive sealing material. Electrode terminals were provided, and a fuel cell unit was produced. The inner electrode terminal had a reduced diameter than the inner diameter of the fuel electrode support serving as a fuel gas flow path, and had a reduced diameter portion extending outward from each end of the cell. A set of 16 fuel cell units was formed, and the 16 fuel cell units were connected in series with a connector connecting the fuel electrode and the air electrode to form a stack. A solid oxide fuel cell module was produced by installing 10 sets of the above stacks, connecting 160 stacks in series, and then surrounding the stack with a housing after attaching a reformer, air piping, and fuel piping. This fuel cell module was incorporated into a solid oxide fuel cell system.

The fuel gas for power generation in the fuel cell system was city gas 13A, and the fuel utilization rate was 75%. In addition, air was used as the oxidizing agent, and the air utilization rate was 40%. S/C=2.25. The steady temperature of power generation was 700° C., and the operation was performed at a current density of 0.2 A/cm ² .

Shutdown of the fuel cell system After two hours of operation at steady temperature, the fuel cell system was shut down by shutting down the supply of electric current, fuel gas, air, and water to the fuel cell system almost simultaneously. Thereafter, the module in the system was taken out, and the appearance of all the solid oxide fuel cells in the module was visually confirmed. As for the cells located inside the fuel cell stack, the cell stack was disassembled and each cell was visually inspected for the presence or absence of cracks in the portion where the air electrode was formed. In addition, the number of floating air electrodes was counted for those with an evaluation of ○, and the number of peeled air electrodes was counted for those that were evaluated as ×.
The appearance was evaluated based on the following criteria.
Evaluation ◎: There is no problem in power generation even after 100 or more shutdowns, and there is no separation of the air electrode or damage to the cell.
Evaluation: Even after less than 100 shutdowns, there was no problem with power generation, and no delamination of the air electrode or cell damage was observed. However, after 100 or more shutdowns, the air Partial lifting (wrinkle) of the pole was confirmed.
Evaluation: ×: Separation of the air electrode was confirmed after the shutdown was stopped less than 5 times.

The above results were as described in Table 1 below.

Examples 2 to 12 and Comparative Examples 1 and 2
Using the raw material powder of (La _0.6 Sr _0.4 ) _A/B (Co _0.2 Fe _0.8 )O ₃ having the A/B ratio shown in Table 1, the sulfur content in the air electrode immediately after firing was adjusted to the amount shown in Table 1. A slurry for an air electrode was prepared by mixing and pulverizing in the same manner as in Example 1, except that sodium dioctyl sulfosuccinate was used as the sulfur compound. Thereafter, a solid oxide fuel cell and a fuel cell system were produced in the same manner as in Example 1. Then, the same test as in Example 1 was conducted. The results were as shown in Table 1.

Claims (4)

air electrode and
a fuel electrode;
A solid oxide fuel cell having a solid electrolyte disposed between the air electrode and the fuel electrode,
The air electrode includes a perovskite oxide, and has a Young's modulus of 10 GPa or more and less than 50 GPa,
In the perovskite oxide,
The A/B ratio, which is the molar ratio between the number of moles contained in the A site (A) and the number of moles contained in the B site (B), is 1.000<A/B ratio≦1.030. Solid oxide fuel cell. The solid oxide fuel cell according to claim 1, wherein the air electrode contains 5 ppm or more and 4000 ppm or less of sulfur element. The perovskite type oxide is
The solid oxide fuel cell according to claim 1 or 2 , wherein the A site contains lanthanum (La) and the B site contains cobalt (Co). The perovskite type oxide is
4. The solid oxide fuel cell according to claim 3 , wherein the solid oxide fuel cell is lanthanum strontium cobalt iron oxide.

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