JP4011771B2 - Solid oxide fuel cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solid oxide fuel cell having a cylindrical shape, and more particularly to a battery cell structure having no interconnector on the outer surface of the cylinder.
[0002]
[Prior art]
The basic structure of a fuel cell is composed of an electrolyte and two electrodes sandwiching both sides thereof. One of the two electrodes is called a fuel electrode, and the other is called an air electrode. A fuel gas such as hydrogen gas is supplied to the fuel electrode from the outside, and an oxidizing gas such as air is supplied to the air electrode from the outside. A fuel cell can directly supply electric energy to the outside in the process of performing an electrochemical reaction for generating water from a fuel gas and an oxidizing gas via an electrolyte.
[0003]
Fuel cells are classified into several types depending on the type of electrolyte material used. A solid oxide fuel cell (SOFC) uses an oxide solid having ionic conductivity as an electrolyte. In order for this oxide solid, that is, a solid electrolyte, to exhibit good ionic conductivity, a high temperature condition is necessary, and therefore, SOFC is usually operated at a temperature condition of 800 ° C. to 1200 ° C.
[0004]
The SOFC is roughly divided into a flat plate type SOFC and a cylindrical type SOFC according to its shape. Cylindrical SOFC has advantages in that it does not have a seal portion in the operation region and has less problems related to sealing, and is less likely to cause warpage or distortion, as compared with a flat plate type.
[0005]
FIG. 2 is a schematic cross-sectional view showing a structural example of a single cell body of a conventional cylindrical SOFC. As shown in the figure, generally, a cylindrical air electrode 101 is used as a support tube, and a solid electrolyte 102 and a fuel electrode 103 are sequentially formed around the outer periphery thereof. On the outer surface, an interconnector 104 that is electrically connected only to the air electrode 101 is formed in a band-like region parallel to the cylindrical major axis direction.
[0006]
Inside the cylindrical air electrode 101, air or oxidizing gas is supplied, and oxygen ions are generated by the action of electrons carried via an external circuit. The oxygen ions are carried to the fuel electrode 103 via the solid electrolyte 102, where they react with hydrogen and generate electrons together with water as a by-product. The electrons are taken into an external circuit and contribute to power generation.
[0007]
The solid electrolyte 102 requires high oxygen ion conductivity, and one surface is in contact with the oxidizing atmosphere and the other surface is in contact with the reducing atmosphere through the air electrode 101 and the fuel electrode 103. It must be chemically stable in both redox atmospheres at operating temperatures. In addition, it is also desired that the material has no electronic conductivity and is excellent in airtightness so as not to pass gas. Generally, stabilized zirconia (YSZ) or the like is selected as a material that satisfies such requirements.
[0008]
The fuel electrode 103 and the air electrode 101 are required to exhibit high electronic conductivity. Further, it is desirable that the thermal expansion coefficient is close to that of the adjacent solid electrolyte 102.
[0009]
Since the fuel electrode 103 is exposed to hydrogen gas, it needs to be chemically stable in a high-temperature reducing atmosphere, and the air electrode 101 is chemically stable in a high-temperature oxidizing atmosphere because it is exposed to air. It is necessary to be.
[0010]
In general, nickel (Ni) and YSZ cermets are used as the fuel electrode 103, and perovskite oxides based on lanthanum cobaltate (LaCoO ₃ ) or lanthanum manganate (LaMnO ₃ ) are selected as the air electrode 101. Often done.
[0011]
[Problems to be solved by the invention]
The conventional cylindrical SOFC main body shown in FIG. 2 has a configuration in which an air electrode, a solid electrolyte, and a fuel electrode are sequentially arranged from the inside, and an interconnector forming region is provided on a part of the outer surface. The present inventors have proposed a cylindrical SOFC (hereinafter, referred to as an interconnector-less SOFC) structure in which an interconnector is eliminated from the cell body.
[0012]
FIG. 3 shows an example of the structure of this interconnectorless SOFC single cell. As shown in the figure, the interconnector-less SOFC shown here has a cylindrical air electrode 114, a solid electrolyte 113, and a fuel electrode 112 as a support from the outside in the order of the layers opposite to the conventional SOFC shown in FIG. Is arranged. These layers are formed with a substantially uniform film thickness.
[0013]
A conductive tube 111 for supplying fuel gas is inserted inside the fuel electrode 112 and in the center of the cylinder. As shown in the figure, in a cell having a structure in which one side of a cylinder is sealed, the conductive tube 111 is inserted to the vicinity of the sealed portion of the cylinder.
[0014]
A gap between the conductive tube 111 and the fuel electrode 112 is filled with a conductive felt 115, for example, Ni felt, and the fuel electrode 112 and the conductive tube 111 are electrically connected. Therefore, the conductive tube 111 is a fuel gas supply pipe and can be used as an external lead electrode (lead) of the fuel electrode 112. The conductive felt 115 is a material that also serves as a catalyst for the reforming reaction that generates hydrogen gas from the fuel gas.
[0015]
According to this configuration, the interconnector is not formed on the outer surface of the cell, and the layers of the solid electrolyte 113 and the fuel electrode 112 are formed as completely concentric continuous films on the inner surface of the air electrode 114. Therefore, there is an advantage that a masking process necessary for forming an interconnector is not required and a wide operation area effective as a battery can be secured. In addition, even as a structure, the bonding surface of the replacement material is reduced, and the stress generated in the operating temperature range from room temperature can be reduced.
[0016]
In general, various fuel gases such as methane (CH ₄ ) gas and carbon dioxide (CO) that can generate hydrogen by a reforming reaction are supplied from the conductive tube 111 into the cylinder together with a small amount of H ₂ O. The The conductive tube 111 is inserted to the edge of the cell reaction region, and as soon as the fuel gas is blown out of the tube, it hits the wall of the cell seal and rebounds there, passing through the gap of the conductive felt 115. However, it returns to the cylindrical opening end on the right side in the figure. During this time, the following reforming reaction proceeds by reaction with water (H ₂ O) at 650 ° C. to 1050 ° C. using the conductive felt 115 as a catalyst, and hydrogen (H ₂ ) gas necessary for the battery reaction is generated. This is generated and supplied to the fuel electrode 112.
[0017]
[Expression 1]
_{CH 4 + H 2 O → CO} + 3H 2 - (1)
[Expression 2]
CO + H ₂ O → CO ₂ + H _2- (2)
The high temperature condition necessary for the reforming reaction is that the battery operating temperature (800 ° C. to 1200 ° C.) satisfies the condition, and the water (H ₂ O) used for the reforming reaction is combined with the fuel gas. Or water obtained as a by-product of the battery reaction.
[0018]
However, the above-described reforming reaction does not proceed uniformly in the long axis direction of the cell cylindrical portion. This is because when the fuel gas blows out from the conductive tube 111 and comes into contact with the Ni felt as a catalyst, most of the reforming reaction of the fuel gas takes place in the vicinity.
[0019]
That is, hydrogen gas that can contribute to the battery reaction has the highest concentration in the vicinity of the gas outlet of the conductive tube, is consumed by the battery reaction as the distance from the outlet increases, and the hydrogen concentration tends to become leaner.
[0020]
Since the concentration of the reaction gas directly affects the progress of the battery reaction, the battery reaction proceeds rapidly in the region where the hydrogen gas concentration is high, and the battery reaction proceeds slowly in the region where the hydrogen gas becomes lean. Become.
[0021]
Since the battery reaction is a reaction accompanied by heat generation, when the reaction proceeds locally, a temperature difference Δt occurs between a region where the battery reaction is active and a region where the battery reaction hardly progresses. When this temperature difference Δt is large, thermal stress due to a difference in volume expansion coefficient is generated inside the cylindrical cell, which may cause cracks or peeling at the layer interface.
[0022]
The present invention has been made in view of the above-described problems, and aims at more uniform generation of battery reactions in a battery reaction region in an interconnector-less cylindrical SOFC.
[0023]
[Means for Solving the Problems]
The solid oxide fuel cell according to claim 1 of the present invention is characterized by a cylindrical air electrode, a solid electrolyte formed on the inner surface of the air electrode, and an inner surface of the solid electrolyte. A fuel electrode, a conductive tube inserted inside the fuel electrode, for supplying fuel gas, and provided in a gap between the conductive tube and the fuel electrode, electrically connecting both of them, and A catalyst material that promotes a reforming reaction, and the fuel electrode minimizes the porosity in the region where the hydrogen gas concentration on the inner surface of the fuel electrode is maximized, and the porosity is reduced as the hydrogen gas concentration decreases. That is to increase.
[0024]
According to the first aspect of the present invention, the porosity of the fuel electrode is small in the vicinity of the fuel gas outlet of the conductive tube where the fuel gas is reformed in large quantities, so that the solid electrolyte passes through the gap in the fuel electrode. Less reformed gas reaches the interface. That is, the hydrogen gas permeability is substantially lowered. On the other hand, in the region where the hydrogen gas concentration is low, away from the fuel gas outlet, the porosity of the fuel electrode is small, so that the hydrogen gas easily reaches the solid electrolyte interface. As a result, the hydrogen concentration at the interface between the solid electrolyte and the fuel electrode can be made uniform regardless of the concentration distribution of the fuel gas concentration on the surface of the fuel electrode. As a result, the battery reaction can proceed uniformly regardless of the location.
[0025]
The solid electrolyte fuel cell according to claim 2 of the present invention is characterized by a cylindrical air electrode, a solid electrolyte formed on the inner surface of the air electrode, and an inner surface of the solid electrolyte. A fuel electrode, a conductive tube inserted inside the fuel electrode, for supplying fuel gas, and provided in a gap between the conductive tube and the fuel electrode, electrically connecting both of them, and A catalyst material that promotes a reforming reaction, and the fuel electrode has a portion with a minimum porosity in a region where the hydrogen gas concentration on the inner surface of the fuel electrode is maximum, and the porosity decreases as the hydrogen gas concentration decreases. Is to reduce.
[0026]
According to the second aspect of the invention, in the region where the concentration of hydrogen gas generated by the reforming reaction of the fuel gas is maximum, the porosity of the fuel electrode is minimized, so that the solid electrolyte passes through the gap in the fuel electrode. The permeability of hydrogen gas, which tends to reach the interface, is substantially reduced. On the other hand, in the region where the hydrogen gas concentration generated by the reforming reaction is low, the porosity of the fuel electrode is increased, so that the hydrogen gas tends to reach the solid electrolyte interface. As a result, regardless of the concentration distribution of the hydrogen gas concentration on the surface of the fuel electrode, the hydrogen concentration at the interface between the solid electrolyte and the fuel electrode can be made uniform regardless of location, and the cell reaction can proceed uniformly regardless of location.
[0027]
In the solid oxide fuel cell having the feature of claim 2, the fuel electrode has a minimum pore in a region where the hydrogen gas concentration on the inner surface of the fuel electrode has a maximum value CHmax. If the porosity is 30 to 40% in the region where the rate Vmin and the hydrogen gas concentration is ½ CHmax, the hydrogen concentration at the solid electrolyte / fuel electrode interface can be made more uniform. it can.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0029]
FIG. 1 is a cell sectional view showing a single cell configuration of a cylindrical interconnector-less SOFC according to an embodiment of the present invention. A cross section parallel to the cell long axis direction is shown on the upper side in the figure, and a cross section perpendicular to the cell long axis direction is shown on the lower side in the figure.
[0030]
Here, an example of a SOFC having a shape in which a cylindrical end portion on one side is sealed is shown. Also in the present embodiment, a configuration similar to that of a conventional interconnector-less SOFC is employed in the battery reaction region. That is, the air electrode 14 is a supporting cylindrical body, the layer of the solid electrolyte 13 is formed on the entire inner surface of the air electrode 14, and the layer of the fuel electrode 12 is formed on the entire inner surface of the solid electrolyte 13.
[0031]
In the center of the cavity inside the fuel electrode 12, a conductive tube 11 for supplying fuel gas is inserted to the vicinity of the cylindrical sealing portion. A gap between the conductive tube 11 and the fuel electrode 12 is filled with a conductive felt 15 serving as a catalyst for the reforming reaction, for example, Ni felt, and the fuel electrode 12 and the conductive tube 11 are electrically connected. . For this reason, the conductive tube 11 is a fuel gas supply pipe and also has a function as a lead electrode (lead) of the fuel electrode 12.
[0032]
The cylindrical interconnector-less SOFC in the present embodiment is greatly different from the conventional one in that the porosity of the fuel electrode is reduced as it goes deeper into the cylindrical cell. That is, the porosity of the fuel electrode 12 in the vicinity of the gas outlet of the conductive tube 11 for supplying the fuel gas is minimized, and the porosity is increased as it goes to the cylindrical opening side of the cell.
[0033]
Also in the case of the cylindrical interconnectorless SOFC in the present embodiment, the conductive tube 11 is inserted to the edge of the battery reaction region, and the fuel gas is blown out from the outlet at the tip of the tube as soon as the cell is blown out. It hits the wall of the sealing part, rebounds there, passes through the gap of the conductive felt 15, and returns to the cylindrical opening end on the right side in the figure.
[0034]
Since the Ni felt that is the conductive felt 15 is also a catalyst for the fuel gas reforming reaction, when the fuel gas blown out from the opening of the conductive tube 11 touches the Ni felt, the formula (1) or (2) is obtained. The reforming reaction shown is caused, and hydrogen (H ₂ ) gas contributing to the battery reaction is generated.
[0035]
Since the reforming reaction occurs most actively in the vicinity of the fuel gas outlet, the concentration of hydrogen gas generated by the reforming reaction is the highest in that region. Gradually dilutes due to consumption.
[0036]
On the other hand, the following cell reaction proceeds between the fuel electrode 12 and the air electrode 14 via the solid electrolyte 13.
[0037]
[Equation 3]
Fuel electrode side: H ₂ + O ²⁻ → H ₂ O + 2e −− (3)
[Expression 4]
Air electrode side: 1 / 2O ₂ + 2e → O ²⁻ −− (4)
Since this cell reaction depends on the reaction gas concentration, if the reaction of the above equation (3) depends on the hydrogen gas concentration on the inner surface of the fuel electrode, a significant difference in the cell reaction rate occurs depending on the location.
[0038]
However, since the battery reaction described above proceeds mainly at the interface between the solid electrolyte 13 and the fuel electrode 12 or the air electrode 14, the hydrogen gas concentration on the surface of the fuel electrode 12 directly affects the battery reaction. Instead, it is the hydrogen gas concentration at the interface between the solid electrolyte 13 and the fuel electrode 12.
[0039]
In the cell according to the embodiment of the present application, the porosity of the fuel electrode 12 in the vicinity of the fuel gas outlet of the conductive tube in which the fuel gas is reformed in a large amount is set to the minimum value Vmin. The porosity is gradually increased. That is, according to the hydrogen gas concentration generated by the reforming reaction on the inner surface of the fuel electrode 12, the porosity of the fuel electrode 12 in the region where the hydrogen gas reaches the maximum value CHmax is set to the minimum Vmin, and the hydrogen gas concentration decreases. The porosity of each region is increased.
[0040]
Note that the porosity in the region where the hydrogen gas concentration on the inner surface of the fuel electrode is 1/2 · CHmax is preferably 30 to 40%.
[0041]
The hydrogen gas permeability at which the hydrogen gas in contact with the inner surface of the fuel electrode 12 reaches the interface of the solid electrolyte 13 through the fuel electrode 12 is the same as the diffusion coefficient of hydrogen gas, the concentration gradient, and the fuel electrode. Depends on porosity etc.
[0042]
According to this configuration, in the region where the hydrogen gas concentration on the inner surface of the fuel electrode is high, the porosity of the fuel electrode 12 is lowered, so that the hydrogen gas permeability is reduced. The amount of hydrogen gas reaching the solid electrolyte interface decreases, and the substantial amount of hydrogen gas that directly contributes to the battery reaction decreases, so that the progress of the battery reaction is suppressed. Since the hydrogen gas consumption here decreases with the suppression of the battery reaction, the concentration of the hydrogen gas on the inner surface of the fuel electrode is somewhat relaxed.
[0043]
On the contrary, in the region where the hydrogen gas concentration on the inner surface of the fuel electrode is low, the porosity of the fuel electrode 12 is increased, so that the hydrogen gas permeability increases and the amount reaching the interface of the solid electrolyte 13 increases. In addition, since the cell reaction is suppressed in a region where the hydrogen gas concentration on the inner surface of the fuel electrode is high, the consumption of hydrogen gas is reduced, and the hydrogen gas concentration on the surface of the fuel electrode is somewhat increased accordingly. The battery reaction is promoted by these influences.
[0044]
As a result, the hydrogen gas concentration at the interface between the fuel electrode 12 and the solid electrolyte 13 is made uniform, and the battery reaction can proceed uniformly regardless of the location in the battery reaction region. That is, uniform power generation can be performed uniformly throughout the battery reaction region, and the power generation efficiency of the cell is increased.
[0045]
Since the battery reaction is an exothermic reaction, if a uniform battery reaction can proceed, a substantially uniform temperature distribution can be obtained in the cell, and the destruction of the cell due to the temperature difference depending on the location can be prevented.
[0046]
Next, a method for manufacturing an interconnector-less SOFC in this embodiment will be briefly described. The basic fabrication process is not different from the conventional interconnector-less SOFC fabrication process.
[0047]
First, a one-side sealed type cylindrical air electrode 14 serving as a support tube is manufactured. That is, lanthanum strontium manganate (LaSrMnO ₃ ) powder having an average particle size of 3 to 10 μm and having a perovskite crystal structure is mixed with water at 20 wt% and methyl cellulose or other binder at 10 wt%, and the whole is kneaded well. Then, after making into a clay, this is processed into a predetermined shape using an extrusion molding method.
[0048]
Furthermore, after drying this, it baked at 1300 degreeC-1500 degreeC for about 5 hours in air | atmosphere atmosphere, and forms a porous sintered compact. The air electrode 14 after sintering is a cylinder with one side sealed, for example, having an outer diameter of about 21 mmΦ, an inner diameter of about 17 mmΦ, and a length of about 500 mm to 900 mm.
[0049]
Next, a layer of the solid electrolyte 13 is formed on the inner wall of the air electrode. For example, when the slurry coating method is used, first, YSZ powder having a particle size of 0.1 μm to 1.0 μm is mixed with a diluent such as ethanol so that the mixing ratio is about 10 wt% to 40 wt%, and about 1 wt. A slurry having a viscosity of 2,000 mPaS to 2,000,000 mPaS is prepared.
[0050]
For example, the above-described slurry is applied to the entire inner peripheral surface of the air electrode 14 using a tubular slurry supply pipe that can be taken in and out of the cylinder of the air electrode 14. At this time, it is preferable to adjust the film thickness by rotating the slurry supply unit at a constant speed so that the thickness is as uniform as possible, or using a screw-like rubber scraper immediately after coating. Thus, the film thickness of the solid electrolyte 13 after coating is set to about 100 μm to 150 μm. Further, after coating, baking is performed at about 1000 ° C. to 1600 ° C. for about 1 to 10 hours to form a dense solid electrolyte layer 13.
[0051]
Next, the fuel electrode 12 is formed on the inner surface of the solid electrolyte 13. The fuel electrode 12 can also be formed by a slurry coating method, similarly to the solid electrolyte 13 described above. As slurry for the fuel electrode, nickel (Ni) powder, cobalt (Co) powder, nickel oxide (NiO) powder, cobalt oxide (CoO) powder or zirconia cermet powder and YSZ powder are mixed in a ratio of 60 wt% to 40 wt%. To produce a mixed powder. Further, the mixed powder and the cellulose-based binder are mixed at 50 wt% to 50 wt% to obtain a slurry having a viscosity of about 1,000 mPaS to 2,000,000 mPaS.
[0052]
Using the tubular slurry supply pipe, the supply part is rotated and moved while flowing the slurry from the supply part at the tip of the supply pipe, and the above slurry is applied to the battery reaction region on the inner surface of the solid electrolyte 13 with a film thickness of about 150 μm. It is applied so as to be ˜300 μm.
[0053]
Thereafter, firing is performed at 1000 ° C. to 1400 ° C. for about 1 hour to 10 hours. At this time, the porosity of each region can be changed by gradually stepping the firing temperature of each region on the cell. . For example, the fuel electrode near the cell sealing portion is fired at about 1300 ° C., and the fuel extreme portion on the cell opening side is fired at about 1100 ° C. By such a method, the porosity of the fuel electrode near the cell sealing portion can be about 10%, and the porosity of the extreme fuel portion on the cell opening side can be about 40%.
[0054]
The porosity of the fuel electrode can also be adjusted by adjusting the particle size of each ceramic powder material to be mixed when forming the slurry. For example, a slurry made of a mixed powder of nickel oxide (NiO) and YSZ whose average particle diameter is adjusted to 5 μm and a slurry made of a mixed powder of NiO and YSZ whose average particle diameter is adjusted to 15 μm are prepared. A fuel electrode having a desired porosity is formed by adjusting the mixing ratio of the slurry. Specifically, in the vicinity of the cell sealing portion, the above slurry having an average particle size of 5 μm is used, and the mixing ratio of the slurry having an average particle size of 15 μm is increased toward the cell opening side. A slurry having an average particle size of about 15 μm is used. As a result, the porosity of the fuel electrode can be about 35% at the open end.
[0055]
After that, as shown in FIG. 1, a cylindrical interconnector-less SOFC can be completed by arranging a conductive felt 15 such as Ni around the conductive tube and inserting it together with the conductive tube 11.
[0056]
In addition, the shape of the cell may be not only one in which one side of the cylinder is sealed, but one in which both sides are open ends. In addition, the fuel gas outlet of the conductive tube is not necessarily provided at one end of the tip, and may be provided at a plurality of locations on the side surface of the tube. In any case, the film thickness of the fuel electrode may be maximized in the region where the hydrogen gas concentration on the inner surface of the fuel electrode is maximized, and the film thickness of each region may be determined according to the density of the hydrogen gas. In addition, the present invention is not limited to the conditions of the above-described embodiment.
[0057]
【The invention's effect】
As described above, the solid oxide fuel cell according to the present invention is characterized in that the porosity of the fuel electrode is close to the fuel gas outlet of the conductive tube in the interconnectorless SOFC having a cylindrical shape. The minimum is that the thickness is reduced according to the distance from the region.
[0058]
In the vicinity of the outlet where the fuel gas is reformed in large quantities and the hydrogen gas concentration is high, the porosity of the fuel electrode is small, so the degree of hydrogen gas reaching the interface with the solid electrolyte through the fuel electrode is substantially reduced. The battery reaction is suppressed. On the other hand, in the region where the hydrogen gas concentration is low, away from the fuel gas outlet, the hydrogen concentration that directly contributes to the cell reaction increases by increasing the porosity of the fuel electrode and making the hydrogen gas easily reach the solid electrolyte interface. , Battery counter-action is promoted.
[0059]
Regardless of the concentration distribution of the hydrogen gas concentration on the surface of the fuel electrode, a uniform cell reaction can proceed in almost the entire cell reaction region, and efficient power generation can be performed. In addition, since the battery reaction involves heat generation, it is possible to make the temperature distribution in the long axis direction of the cylindrical cell uniform, suppress the generation of thermal stress due to temperature differences, and prevent cracking and delamination on the support. This can prevent the battery life.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a cylindrical SOFC device according to an embodiment of the present invention.
FIG. 2 is a perspective view of an apparatus showing a single cell structure of a conventional cylindrical SOFC.
FIG. 3 is an apparatus cross-sectional view showing a single cell structure of a conventional cylindrical interconnector-less SOFC.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Conductive tube 12 ... Fuel electrode 13 ... Solid electrolyte 14 ... Air electrode 15 ... Conductive felt

Claims (3)

An air electrode having a cylindrical shape;
A solid electrolyte formed on the inner surface of the air electrode;
A fuel electrode formed on the inner surface of the solid electrolyte;
A conductive tube inserted inside the fuel electrode and supplying fuel gas;
A catalyst material that is provided in a gap between the conductive tube and the fuel electrode, electrically connects both, and promotes a reforming reaction of the fuel gas;
The fuel electrode is
A solid oxide fuel cell characterized in that the porosity of a region near the fuel gas outlet of the conductive tube is minimized and the porosity is gradually increased according to the distance from the region. An air electrode having a cylindrical shape;
A solid electrolyte formed on the inner surface of the air electrode;
A fuel electrode formed on the inner surface of the solid electrolyte;
A conductive tube inserted inside the fuel electrode and supplying fuel gas;
A catalyst material that is provided in a gap between the conductive tube and the fuel electrode, electrically connects both, and promotes a reforming reaction of the fuel gas;
The fuel electrode is
A solid oxide fuel cell characterized in that the porosity in a region where the hydrogen gas concentration on the inner surface of the fuel electrode is maximum is minimized and the porosity is increased as the hydrogen gas concentration decreases. The fuel electrode is
A region where the hydrogen gas concentration on the inner surface of the fuel electrode has a maximum value CHmax has a minimum porosity Vmin;
3. The solid oxide fuel cell according to claim 2, having a porosity of 30 to 40% in a region where the hydrogen gas concentration is ½ CHmax.

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