JP2013235710A - Solid oxide fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid oxide fuel cell that operates at a high temperature and reforms fuel gas internally and that prevents a decrease in durability due to thermal stress and also improves a decline in power generation performance.SOLUTION: A solid oxide fuel cell includes: a cathode electrode 102; an anode electrode 104; a solid electrolyte 103 that is arranged between the cathode electrode 102 and the anode electrode 104; and a fuel gas passage 107 through which fuel gas passes. A porous layer 105 formed of a porous material is provided adjacent to the anode electrode 104. A reforming reaction layer 106 that reforms fuel gas is provided adjacent to the porous layer 105. The fuel gas passage 107 is provided adjacent to the reforming reaction layer 106.

Description

  The present invention relates to a fuel cell having a solid electrolyte, and more particularly to a solid oxide fuel cell.

  A fuel cell includes an anode (fuel electrode) and a cathode (air electrode) with an electrolyte sandwiched between them. Fuel gas is supplied to the anode side, oxidant gas is supplied to the cathode side, and fuel and oxidant are supplied via the electrolyte. It is a power generator that generates electricity by electrochemical reaction. A solid oxide fuel cell (SOFC), which is one of the types of fuel cells, is a fuel cell that has high power generation efficiency and operates at a high temperature of 600 to 1000 ° C. There is a feature that can be done. For this reason, fuel can be diversified by internal reforming, and has the potential to reduce costs compared to other fuel cells.

  In a high-temperature operation type fuel cell, the fuel reforming reaction performed inside the cell (cell) using methane as the fuel is an endothermic reaction with a fast reaction rate as shown in the equation (1), and the electrochemical reaction at the anode electrode The reaction is an exothermic reaction represented by formula (2).

CH ₄ + 2H ₂ O → 4H ₂ + 2CO ₂ +165 kJ / mol (1)
H ₂ + 1 / 2O ₂ → H ₂ O-242 kJ / mol (2)
For this reason, a temperature gradient is locally generated inside the cell, and there is a risk of failure due to thermal stress. Further, in the hydrogen production process from methane by the steam reforming reaction, carbon may be produced and precipitated by the dehydrogenation heavy bond shown in the formula (3). The deposition of carbon causes a decrease in catalytic activity at the anode electrode and a blockage of the fuel gas transport path, leading to a decrease in cell performance.

CH ₄ + CH ₄ → 4H ₂ + 2C (3)
As conventional techniques for internal reforming in a high-temperature operating fuel cell, Patent Documents 1 and 2 disclose a fuel cell in which a dedicated porous reforming catalyst layer in charge of a reforming reaction is provided on an anode electrode. Yes. Patent Document 3 and Patent Document 4 include a fuel cell in which a catalyst layer that performs a reforming reaction is provided inside a guide tube that supplies fuel gas to the anode electrode layer, and the reforming reaction is performed inside the guide tube. It is disclosed.

JP 2001-035507 A JP 2003-086226 A JP 2008-108647 A JP 2006-332027 A

  In a fuel cell that performs a reforming reaction inside the guide tube, a guide tube that supplies fuel gas to the anode electrode layer is installed inside the cylindrical cell, so that the diameter of the cylindrical cell increases. As a result, the ohmic loss increases due to the increase in the current path, and there is a problem in the power generation performance. Furthermore, since the volume of the cylindrical cell increases, it is difficult to improve the volume output density.

  On the other hand, in a fuel cell in which a dedicated porous reforming catalyst layer in charge of a reforming reaction is provided on an anode electrode, a cylindrical cell is composed of a fuel gas channel, a porous reforming catalyst layer, an anode electrode, an electrolyte, and a cathode electrode. It can be constructed in order and can be made compact, and it is possible to prevent the expansion of ohmic loss due to the increase of the current path and to improve the volume output density. However, since the anode electrode and the porous reforming catalyst layer are adjacent to each other, a local temperature gradient is generated due to a large endothermic effect accompanying the reforming reaction in the vicinity of the anode electrode, and the anode electrode and the electrolyte are mechanically affected by thermal stress. receive damage. In addition, the local endothermic effect associated with the reforming reaction causes the temperature to decrease and the overvoltage of the electrode reaction to increase at the anode electrode, which increases the energy required for the electrode reaction and causes performance degradation. Furthermore, in the porous reforming catalyst layer adjacent to the anode electrode, carbon is deposited along with the reforming reaction, and the deposited carbon blocks the fuel gas transport path to the vicinity of the electrode and reduces the activity of the electrode reaction. Since it induces, the power generation performance of the cell may be reduced.

  As described above, the conventional high-temperature operation type fuel cell that internally reforms the fuel gas has the problems of lowering durability due to thermal stress and lowering power generation performance.

  An object of the present invention is to provide a solid oxide fuel cell that internally reforms a fuel gas and that can prevent a decrease in durability due to thermal stress and reduce a decrease in power generation performance in a solid oxide fuel cell A fuel cell is provided.

  A solid oxide fuel cell according to the present invention comprises a cathode electrode, an anode electrode, a solid electrolyte disposed between the cathode electrode and the anode electrode, and a fuel gas passage through which fuel gas flows. In the physical fuel cell, a porous layer composed of a porous body is provided adjacent to the anode electrode, a reforming reaction layer for reforming the fuel gas is provided adjacent to the porous layer, The fuel gas flow path is provided adjacent to the reforming reaction layer.

  According to the present invention, in a high temperature operation type solid oxide fuel cell in which fuel gas is internally reformed, it is possible to prevent a decrease in durability due to thermal stress and reduce a decrease in power generation performance.

1 is a partial cross-sectional view of a solid oxide fuel cell according to an embodiment of the present invention. 1 is a schematic diagram of a solid oxide fuel cell according to an embodiment of the present invention, showing a cross section of a cylindrical cell. It is a schematic diagram of the solid oxide fuel cell by another Example of this invention, and is a figure which shows the cross section of a cylindrical cell. It is a schematic diagram of the solid oxide fuel cell by another Example of this invention, and is a figure which shows the cross section of a cylindrical cell. It is a figure which shows the simulation analysis model of the cylindrical fuel cell by a prior art, and is a figure which shows a cross section perpendicular | vertical to the length direction of a fuel cell. It is a figure which shows the simulation analysis model of the cylindrical fuel cell by a present Example, and is a figure which shows a cross section perpendicular | vertical to the length direction of a fuel cell. Table showing analysis conditions for simulation analysis. It is a figure which shows the analysis result of simulation analysis, and is a figure which shows the temperature distribution of the cross section perpendicular | vertical to the length direction of a cylindrical fuel cell. The graph which shows the temperature distribution in the cross section perpendicular | vertical to a length direction about the fuel cell by a prior art, and the fuel cell by a present Example. The figure which shows an example of the flow-path shape of the fuel gas flow path of a fuel cell. FIG. 10B is a cross-sectional view of a cylindrical fuel cell in which the flow path shape of the fuel gas flow path is the flow path shape 1009 shown in FIG. The figure which shows another example of the flow-path shape of the fuel gas flow path of a fuel cell. FIG. 11B is a cross-sectional view of a cylindrical fuel cell in which the fuel gas flow channel shape is the flow channel shape 1010 shown in FIG. 11A.

  The solid oxide fuel cell according to the present invention is a high-temperature operation type fuel cell that internally reforms fuel gas, such as electrode peeling and cracks in the solid electrolyte due to thermal stress caused by the endothermic action accompanying the internal reforming reaction. Mechanical damage can be reduced. Furthermore, since a local electrode temperature drop caused by the endothermic effect can be prevented, an increase in electrode reaction overvoltage caused by this temperature drop can be prevented, and a drop in fuel cell performance can be suppressed. Furthermore, it is possible to suppress a decrease in power generation performance due to a decrease in the activity of the electrode catalyst due to carbon deposition accompanying an internal reforming reaction or a blockage of a fuel gas transport path to the electrode. Therefore, the solid oxide fuel cell according to the present invention can prevent a decrease in durability due to thermal stress and reduce a decrease in power generation performance.

  In the solid oxide fuel cell according to the present invention, a porous layer is provided adjacent to the electrode (anode), and a reforming reaction layer is provided adjacent to the porous layer. For this reason, when the cell is cylindrical, it is not necessary to introduce a guide tube provided with a reforming reaction layer inside the cell, and the cell diameter does not increase, so that a compact cell can be produced.

  In addition, since a porous layer is provided between the anode electrode and the reforming reaction layer, the anode electrode causing the exothermic reaction and the reforming reaction layer causing the endothermic reaction can be isolated and a distance can be provided between them. . For this reason, local temperature gradients due to exothermic and endothermic effects can be relaxed, and even if mechanical damage due to thermal stress occurs, the porous layer acts as a buffer layer and absorbs this damage. It is possible to suppress electrode peeling and cracking of the solid electrolyte.

  In addition, since the porous layer serves as a filter for carbon produced by the reforming reaction, it is possible to suppress deposition on the anode electrode layer. For this reason, it is possible to prevent a decrease in catalytic activity in the anode electrode layer and a blockage of the fuel gas transport path due to the deposition of carbon accompanying the internal reforming reaction.

  Hereinafter, solid oxide fuel cells according to embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a partial cross-sectional view of a solid oxide fuel cell according to an embodiment of the present invention. The solid oxide fuel cell according to this embodiment includes a cathode electrode 102, a solid electrolyte 103, an anode electrode 104, a porous layer 105, a reforming reaction layer 106, and a fuel gas channel 107. As shown in FIG. 1, the reforming reaction layer 106 is disposed on the fuel gas channel 107, the porous layer 105 is disposed on the reforming reaction layer 106, and the anode electrode 104 is disposed on the porous layer 105. The solid electrolyte 103 is disposed on the anode electrode 104, and the cathode electrode 102 is disposed on the solid electrolyte 103. The solid electrolyte 103 is sandwiched between the cathode electrode 102 and the anode electrode 104. The solid oxide fuel cell according to this embodiment is characterized in that a porous layer 105 is disposed between the anode electrode 104 and the reforming reaction layer 106.

The fuel gas channel 107 may be a porous layer. Materials include silicon nitride (Si ₃ N ₄ ), silicon carbide (SiC), zirconia (ZrO ₂ ), alumina (Al ₂ O ₃ ), mullite (3Al ₂ O ₃ · SiO ₂ ), cordierite (2MgO · Fine ceramics having excellent thermal shock resistance, such as 2Al ₂ O ₃ · 5SiO ₂ , having a porosity of 30% or more is desirable. In order to have strength as a support, the porosity is desirably 30% to 95%.

  The reforming reaction layer 106 is composed of a porous body containing a steam reforming catalyst, and reforms the fuel gas according to the reforming reaction shown in the formula (1). As the porous body, a porous material made of fine ceramics, a porous cermet material, or a porous film similar to the fuel gas channel 107 can be used. As the steam reforming catalyst, platinum, palladium, ruthenium, rhodium, vanadium, nickel, or an alloy thereof can be used. The reforming reaction layer 106 preferably has a porosity of 30% or more and a thickness of 50 μm or more. Considering the strength, the porosity is preferably 30% to 95%.

The porous layer 105 is composed of a porous body that does not contain a steam reforming catalyst. Like the fuel gas flow path 107, the porous body includes silicon nitride (Si ₃ N ₄ ), silicon carbide (SiC), zirconia (ZrO ₂ ), alumina (Al ₂ O ₃ ), mullite (3Al ₂ O _3. Fine ceramics excellent in thermal shock resistance such as SiO ₂ ) and cordierite (2MgO · 2Al ₂ O ₃ · 5SiO ₂ ) can be used. A porous cermet material can also be used. The porous body is preferably composed mainly of zirconia (ZrO ₂ ) or silicon nitride (Si ₃ N ₄ ) having a low thermal conductivity.

  The porosity of the porous layer 105 is preferably 30% or more in consideration of the diffusibility of fuel gas, strength, and electrical resistance. In particular, in order to have strength as a support, 30% to 95% is desirable.

  When the thickness of the porous layer 105 is 10 times or more the thickness of the anode electrode 104, an effect of isolating the anode electrode 104 and the reforming reaction layer 106 (effect as a buffer layer and a filter) is obtained. Since the thickness of the anode electrode 104 may be reduced to about 10 μm in order to reduce the electric resistance, the thickness of the porous layer 105 is desirably 100 μm or more. The upper limit value of the thickness of the porous layer 105 can be determined according to the specifications of the fuel cell.

  Thus, by giving the porous layer 105 a thickness of 100 μm or more, the reforming reaction layer 106 and the anode electrode 104 can be isolated and a distance can be provided between them. Thereby, the influence of the endothermic effect in the reforming reaction layer 106 is prevented from directly reaching the anode electrode 104, and the peeling of the anode electrode 104 and the cracking of the solid electrolyte 103 caused by the thermal stress due to the local temperature gradient are suppressed. be able to. In addition, since the porous layer 105 is provided between the anode electrode 104 and the reforming reaction layer 106, adverse effects caused by carbon deposition in the reforming reaction layer 106, that is, a decrease in catalyst activity at the anode electrode 104 and fuel gas It is possible to prevent the transportation route from being blocked.

  FIG. 2 is a schematic view of a solid oxide fuel cell according to an embodiment of the present invention, showing a cross section of a cylindrical cell. In this embodiment, a fuel cell having a cylindrical cell is shown as an example. The solid oxide fuel cell according to the present embodiment can take any shape, and may be, for example, a flat plate shape, a cylindrical shape, a flat cylindrical shape (including an elliptical shape), a rectangular parallelepiped shape, or a cubic shape. . The solid oxide fuel cell according to this example is characterized in that a porous layer is disposed between the anode electrode and the reforming reaction layer, and is effective regardless of the shape of the cell.

  When the cell has a cylindrical shape or a flat cylindrical shape, electrodes are arranged on the inner surface and the outer surface of the cylindrical or flat cylindrical solid electrolyte. The anode is disposed on one of the inner surface and the outer surface of the solid electrolyte, and the cathode is disposed on the other. Whether the anode is disposed on the inner surface or the outer surface of the solid electrolyte can be arbitrarily selected. In this embodiment, as shown in FIG. 2, a solid oxide fuel cell (fuel cell) having an anode on the inner surface of the solid electrolyte and a cathode on the outer surface will be described.

  In FIG. 2, the fuel cell 200 includes a cylindrical solid electrolyte 203, a cathode electrode 202 is provided on the outer surface of the solid electrolyte 203, and an anode electrode 204 is provided on the inner surface of the solid electrolyte 203. Inside the anode electrode 204, a porous layer 205 is disposed adjacent to the anode electrode 204. Inside the porous layer 205, a reforming reaction layer 206 is disposed adjacent to the porous layer 205. A fuel gas flow path 207 is disposed inside the reforming reaction layer 206 adjacent to the reforming reaction layer 206. The fuel gas channel 207 has a cylindrical shape and exists in the central portion of the fuel cell 200 in the radial direction. Further, the fuel cell 200 is provided with an interconnector 201 for taking out the current of the anode electrode 204 to the outside. The interconnector 201 is electrically connected to the anode electrode 204. The fuel gas flows through the fuel gas passage 207, and the oxidant gas flows along the cathode electrode 202 on the outer periphery of the fuel cell 200.

  For example, natural gas can be used as the fuel gas. Natural gas is a mixed gas containing methane and water vapor as main components. In the reforming reaction layer 206, hydrogen and carbon dioxide are generated from the fuel gas flowing in the fuel gas flow path 207 by the steam reforming reaction shown in Expression (1). The generated hydrogen is supplied to the anode electrode 204 via the porous layer 205. In the anode electrode 204, electric energy is generated by the electrochemical reaction shown in Formula (2).

  The solid oxide fuel cell according to this embodiment is characterized in that a porous layer 205 is disposed between the anode electrode 204 and the reforming reaction layer 206. The porous layer 205 suppresses the endothermic action of the steam reforming reaction represented by the formula (1) from being transmitted to the anode electrode 204 and the solid electrolyte 203. Therefore, the porous layer 205 can prevent the anode electrode 204 and the solid electrolyte 203 from being mechanically damaged by thermal stress. Further, the porous layer 205 serves as a filter and can suppress the carbon generated by the reforming reaction from being deposited on the anode electrode 204. Therefore, the porous layer 205 suppresses a decrease in power generation performance due to a decrease in the activity of the electrode catalyst due to carbon deposition accompanying the reforming reaction or a blockage of a fuel gas transport path to the electrode. Can do.

In this example, the approximate dimensions of the cylindrical fuel cell 200 were a diameter of 16 mm, a length of 800 mm, and a power generation area of 252 cm ² .

  In order to give the fuel gas channel 207 strength as a support substrate, a silicon nitride ceramic porous body was used. The silicon nitride ceramic porous body as the fuel gas flow path 207 was produced as follows. A sintering aid is added to and mixed with the silicon nitride ceramic powder, and a powder of pore-forming material of short fibers that can be incinerated is added to the mixture, and a molded body is produced by water-based slurry casting. The dispersed short fibers were incinerated and removed by heating under an active gas to obtain a silicon nitride ceramic porous body. The produced silicon nitride ceramic porous body has fibrous through pores, has a porosity of 85%, and a diameter of 4 mm.

  The reforming reaction layer 206 was produced by forming a porous layer of Ni—YSZ cermet having a porosity of 60% and a thickness of 0.5 mm around the fuel gas channel 207.

  The porous layer 205 was produced by forming a silicon nitride ceramic porous body having a porosity of 85% and a thickness of 4.5 mm around the reforming reaction layer 206. The silicon nitride ceramic porous body as the porous layer 205 was produced as follows. A silicon nitride ceramic powder is mixed with a sintering aid, and an incinerated short fiber pore-forming material slurry is applied to the mixture, and the dispersed short fibers are incinerated by heating under an inert gas. This was removed to obtain a silicon nitride ceramic porous body.

  For the anode electrode 204, a porous cermet made of nickel and YSZ and having a thickness of 495 μm was used.

  The solid electrolyte 203 was produced by forming a 10 μm thick layer around the anode electrode 204. As the material of the solid electrolyte 203, for example, yttrium stabilized zirconia (YSZ) can be used.

  As the cathode electrode 202, lanthanum manganate having a thickness of 495 μm was used.

  Lanthanum chromide was used for the interconnector 201.

  FIG. 3 is a schematic view of a solid oxide fuel cell according to another embodiment of the present invention, showing a cross section of a cylindrical cell. The fuel cell 300 according to this embodiment is similar to the fuel cell 200 shown in FIG. 2 in that the fuel gas channel 307, the reforming reaction layer 306, the porous layer 205, the anode electrode 204, the solid electrolyte 203, and the cathode electrode. 202 and an interconnector 201. Since the porous layer 205, the anode electrode 204, the solid electrolyte 203, the cathode electrode 202, and the interconnector 201 of the fuel cell 300 are the same as or correspond to those of the fuel cell 200 shown in FIG. Omitted. Hereinafter, the fuel gas channel 307 and the reforming reaction layer 306 will be described.

  In the fuel cell 300 according to this embodiment, the fuel gas channel 307 has a star-shaped cross section perpendicular to the length direction. That is, the shape (flow channel shape) of the cross section perpendicular to the length direction of the fuel gas flow channel 307 is a polygon (star shape) having protrusions protruding radially. The reforming reaction layer 306 also has a star-shaped inner periphery and outer periphery in a cross section perpendicular to the length direction in accordance with the flow path shape of the fuel gas flow path 307. By forming the fuel gas channel 307 and the reforming reaction layer 306 in such a shape, the reaction area of the reforming reaction layer 306 can be increased.

  The reaction rate (unit: Mol / sec) of the steam reforming reaction shown in the equation (1) depends on the reaction area of the reforming reaction layer 306 and the flow rate of the fuel gas flowing through the fuel gas channel 307. The flow rate of the fuel gas flowing through the fuel gas channel 307 depends on the cross-sectional area (channel cross-sectional area) perpendicular to the length direction of the fuel gas channel 307. Therefore, the reaction area of the reforming reaction layer 306 and the cross-sectional area of the fuel gas channel 307 are adjusted by changing the shape of the fuel gas channel 307 and the shape of the inner periphery of the reforming reaction layer 306. The reaction rate of the steam reforming reaction can be controlled.

  Hereinafter, an example will be described in which the reaction rate of the steam reforming reaction shown in Formula (1) is controlled by changing the shapes of the fuel gas flow path and the reforming reaction layer.

  FIG. 10A is a diagram illustrating an example of the flow path shape of the fuel gas flow path 307 of the fuel battery cell 300. The channel shape 1008 shown in the upper diagram of FIG. 10A is the same shape as the channel shape of the fuel gas channel 307 shown in FIG. By changing the flow path shape of the fuel gas flow path 307 to the flow path shape 1009 shown in the lower part of FIG. 10A by making the concave portion of the flow path shape 1008 a protrusion (indicated by a dotted line in the drawing). The flow path cross-sectional area of the fuel gas flow path 307 can be increased without changing the reaction area of the mass reaction layer 306.

  FIG. 10B is a cross-sectional view of a cylindrical fuel cell 1000 in which the flow path shape of the fuel gas flow path 1007 is the flow path shape 1009 shown in FIG. 10A. 10B, the same reference numerals as those in FIG. 3 denote the same or corresponding elements as those in FIG. 3, and the description thereof will be omitted. The shape of the inner periphery and the outer periphery of the reforming reaction layer 1006 of the fuel battery cell 1000 is a star shape that matches the channel shape 1009 of the fuel gas channel 1007.

  In the fuel cell 1000, the reaction area of the reforming reaction layer 1006 does not change. Since the cross-sectional area of the fuel gas channel 1007 is larger than that of the fuel gas channel 307 of the fuel battery cell 300 shown in FIG. 3, the flow rate of the fuel gas is reduced, and the fuel gas is separated from the reforming reaction layer 1006. Therefore, when the flow path shape 1009 is used for the fuel gas flow path 1007, the steam reforming reaction is performed more in the reforming reaction layer 1006 than the fuel cell 300 in FIG. Speed can be increased.

  FIG. 11A is a diagram showing another example of the flow path shape of the fuel gas flow path 307 of the fuel battery cell 300. The channel shape 1008 shown in the upper diagram of FIG. 11A is the same as the channel shape of the fuel gas channel 307 shown in FIG. By modifying the flow path shape of the fuel gas flow path 307 to the flow path shape 1010 shown in the lower diagram of FIG. 11A, the protrusions of the flow path shape 1008 are lengthened (indicated by dotted lines in the figure). The reaction area of the reaction layer 306 can be increased.

  FIG. 11B is a cross-sectional view of a cylindrical fuel cell 1100 in which the flow path shape of the fuel gas flow path 1107 is the flow path shape 1010 shown in FIG. 11A. 11B, the same reference numerals as those in FIG. 3 denote the same or corresponding elements as those in FIG. 3, and the description thereof will be omitted. The shape of the inner periphery and the outer periphery of the reforming reaction layer 1106 of the fuel battery cell 1100 is a star shape that matches the channel shape 1010 of the fuel gas channel 1107.

  In the fuel cell 1100, the reaction area of the reforming reaction layer 1106 is larger than that of the reforming reaction layer 306 of the fuel cell 300 shown in FIG. Will increase. Therefore, when the flow path shape 1010 is used for the fuel gas flow path 1107, compared with the fuel battery cell 300 of FIG. 3, more steam reforming reaction is performed in the reforming reaction layer 1006, and the reaction rate can be increased. .

  As described above, in the fuel cell according to the present embodiment, the flow rate of the fuel gas and the reaction area of the reforming reaction layer can be adjusted by changing the shapes of the fuel gas flow path and the reforming reaction layer. It is possible to control the reaction rate of the steam reforming reaction shown in FIG.

  Further, the flow rate of the fuel gas can be adjusted by changing the cross-sectional area of the fuel gas flow channel without changing the flow channel shape of the fuel gas flow channel. For example, when the diameter of the fuel gas flow path 207 of the fuel cell 200 shown in FIG. 2 is increased, the flow rate of the fuel gas is decreased, and the time during which the fuel gas contacts the reforming reaction layer 206 is increased. When the diameter of the gas channel 207 is increased to increase the channel cross-sectional area, a large amount of steam reforming reaction is performed in the reforming reaction layer 206, and the reaction rate can be increased.

  FIG. 4 is a schematic view of a solid oxide fuel cell according to still another embodiment of the present invention, and shows a cross section of a cylindrical cell. 4, the same reference numerals as those in FIG. 2 denote the same or corresponding elements as those in FIG. 2, and the description thereof will be omitted. The fuel cell 400 according to this embodiment includes a plurality of fuel gas flow paths 407, and each fuel gas flow path 407 is surrounded by a reforming reaction layer 406. The plurality of fuel gas flow paths 407 surrounded by the reforming reaction layer 406 are arranged dispersed in the porous layer 205. Accordingly, the plurality of fuel gas flow paths 407 are scattered inside the fuel battery cell 400.

  As described above, by dispersing the plurality of fuel gas flow paths 407 surrounded by the reforming reaction layer 406 inside the fuel cell 400, the fuel gas flow non-uniformity and the electrode reaction non-uniformity are suppressed. Can do. The number and arrangement of the fuel gas flow paths 407 surrounded by the reforming reaction layer 406 can be arbitrarily determined according to the specifications of the fuel cell 400. However, it is preferable to arrange the fuel gas flow path 407 symmetrically with respect to the central axis of the fuel cell 400 from the viewpoint of suppressing fuel gas flow and electrode reaction non-uniformity.

  Even when the plurality of fuel gas flow paths 407 are scattered inside the fuel cell 400, the shapes of the fuel gas flow paths 407 and the reforming reaction layer 406 are as shown in FIGS. 3, 10B, and 11B. Moreover, it can also be made into shapes other than a cylindrical shape. The shapes of the respective fuel gas passages 407 and the reforming reaction layer 406 may be all the same or different from each other. Also, the diameters of the respective fuel gas passages 407 may all be the same or different from each other.

  The shape of the fuel gas channel and the reforming reaction layer, the channel cross-sectional area of the fuel gas channel, and the number and arrangement of the fuel gas channels may not be constant in the length direction of the fuel cell. That is, according to the position in the length direction of the fuel cell, at least one of the shape of the fuel gas flow path and the reforming reaction layer, the cross-sectional area of the fuel gas flow path, and the number and arrangement of the fuel gas flow paths One may be changed.

  For example, the shape of the fuel gas channel and the reforming reaction layer in the center of the length direction of the fuel cell is the shape of the fuel gas channel 307 and the reforming reaction layer 306 (star shape) in FIG. The shape of the fuel gas channel and the reforming reaction layer at the end in the length direction of the cell (for example, in the vicinity of the fuel gas inlet), and the shape of the fuel gas channel 207 and the reforming reaction layer 206 in FIG. By doing so, the speed of the reforming reaction at the center in the length direction can be made faster than at the end in the length direction.

  Further, for example, the shape of the fuel gas flow path and the reforming reaction layer in the center of the length direction of the fuel cell is the shape of the fuel gas flow path 1007 and the reforming reaction layer 1006 in FIG. The shapes of the fuel gas channel and the reforming reaction layer at the end in the length direction (for example, in the vicinity of the fuel gas inlet) are the shapes of the fuel gas channel 307 and the reforming reaction layer 306 in FIG. That is, the fuel gas channel has a star shape, but the star shape is changed at the center and the end in the length direction (the number of protrusions is changed). By doing in this way, the speed | rate of the reforming reaction in the center part of a length direction can be made faster than the edge part of a length direction. The star shape may change not only the number of protrusions but also the length of the protrusions at the center and the end in the length direction (see FIG. 11B).

  Further, for example, by making the flow path cross-sectional area of the center portion in the length direction of the fuel cell larger than the flow path cross-sectional area of the end portion in the length direction of the fuel cell, the center portion in the length direction The speed of the reforming reaction can be made faster than the lengthwise ends. In addition, for example, the number of fuel gas channels is one at the end of the fuel cell in the length direction, and the number of fuel gas channels branches off toward the center in the length direction of the fuel cell. By making it increase, the speed | rate of the reforming reaction in the center part of a length direction can also be made faster than the edge part of a length direction.

  The shape of the fuel gas flow path and the reforming reaction layer, the cross-sectional area of the fuel gas flow path, and the number and arrangement of the fuel gas flow paths are changed continuously (slowly) in the length direction of the fuel cell. It may be changed discontinuously (abruptly).

  As described above, in the fuel cell according to the present embodiment, the reaction rate of the steam reforming reaction represented by the formula (1) can be controlled according to the position in the length direction of the fuel cell.

  Next, the effect of the present embodiment is shown by analysis using numerical simulation. In the simulation analysis, a cylindrical fuel battery cell was analyzed. In order to clarify the effects of the invention, simulations were carried out for two cases of the conventional fuel cell and the fuel cell according to this example. The effectiveness of this example was verified by comparing the temperature distribution in the cross section perpendicular to the length direction of each fuel cell.

  FIG. 5 is a diagram showing an analysis model of a cylindrical fuel cell according to the prior art, and shows a cross section perpendicular to the length direction of the fuel cell. As shown in FIG. 5, the fuel cell analysis model according to the prior art includes a fuel gas channel 507, a reforming reaction layer 506, an anode electrode 504, a solid electrolyte 503, and a cathode electrode 502 from the center in the radial direction. Prepare in order. Further, an interconnector 501 for taking out the current of the anode electrode 504 to the outside is electrically connected to the anode electrode 504, and a current collector plate 509 for flowing a current to the cathode electrode 502 is electrically connected to the cathode electrode 502.

  The fuel battery cell had a cylindrical shape with a diameter of 16 mm and a length of 800 mm. In FIG. 5, the length direction is a direction perpendicular to the paper surface. The fuel gas flow path 507 was a cylindrical region having a diameter of 13 mm and a length of 800 mm. The reforming reaction layer 506 was a Ni—YSZ cermet material having a thickness of 0.5 mm and a porosity of 60%. The anode electrode 504 was a Ni-YSZ cermet material having a thickness of 0.495 mm and a porosity of 30%. The solid electrolyte 503 was a YSZ material having a thickness of 10 μm and an electric resistance of 0.05 Ωm. The cathode electrode 502 was a lanthanum manganate material having a thickness of 0.495 mm and a porosity of 30%. The total thickness of the anode electrode 504, the solid electrolyte 503, and the cathode electrode 502 is 1.0 mm. The fuel battery cell is surrounded by an air flow path 508. The air flow path 508 is a region through which an oxidant gas, that is, air flows, and has a width of 20 mm, a height of 20 mm, and a length of 800 mm.

  FIG. 6 is a diagram showing an analysis model of a cylindrical fuel cell according to the present embodiment, and shows a cross section perpendicular to the length direction of the fuel cell. As shown in FIG. 6, the fuel cell analysis model according to the present embodiment includes a fuel gas channel 607, a reforming reaction layer 606, a porous layer 605, an anode electrode 604, a solid electrolyte 603, and a cathode electrode 602. Provided in this order from the radial center. Further, an interconnector 601 for taking out the current of the anode electrode 604 to the outside is electrically connected to the anode electrode 604, and a current collector plate 609 for flowing a current to the cathode electrode 602 is electrically connected to the cathode electrode 602.

  The size and material of the fuel cell, the anode electrode 604, the solid electrolyte 603, the cathode electrode 602, and the air flow path 608 are the same as those of the conventional cylindrical fuel cell analysis model shown in FIG. .

  The fuel gas channel 607 was a rectangular region having a width of 4 mm, a height of 4 mm, and a length of 800 mm. The reforming reaction layer 606 disposed outside the fuel gas channel 607 was a square region having a thickness of 0.5 mm, and was a Ni—YSZ cermet material having a porosity of 60%. The reason why the fuel gas channel 607 and the reforming reaction layer 606 are modeled in a rectangular region is for the convenience of creating a mesh used for the simulation, and the shape of these regions may not be a rectangle. For example, a circular shape as shown in FIG. 2 or a star shape as shown in FIGS. 3, 10B and 11B may be used. Even if these regions are circular or star-shaped, the same results as shown below can be obtained.

  The porous layer 605, which is a feature of this embodiment, is disposed between the reforming reaction layer 606 and the anode electrode 604. The porous layer 605 was modeled by using a silicon nitride ceramic porous material with a porosity of 85% in a region having a diameter of 14 mm and a length of 800 mm surrounding the fuel gas flow path 607 and the reforming reaction layer 606.

  For the simulation, ANSYS Fluent thermal fluid analysis software was used.

FIG. 7 shows the analysis conditions for the simulation analysis. As shown in FIG. 7, the operating current density was 0.4 A / cm ² . As the fuel gas, methane 50% reformed gas was used, the fuel utilization rate was 75%, the steam-carbon ratio was 2: 1, and the inlet temperature was 600 ° C. Air was used as the oxidant gas, the oxygen utilization rate was 20%, and the inlet temperature was 600 ° C. The flow direction of the fuel gas and the oxidant gas was counterflow, and the wall surface was insulated.

  FIG. 8 is a diagram showing an analysis result of the simulation analysis, and is a diagram showing a temperature distribution in a cross section perpendicular to the length direction of the cylindrical fuel cell. The left figure of FIG. 8 shows the temperature distribution 810 of the cylindrical fuel cell by a prior art, and the right figure shows the temperature distribution 820 of the cylindrical fuel cell by a present Example.

  As can be seen from the temperature distribution 810 of the cylindrical fuel cell according to the prior art, the temperature of the air channel region 818 and the fuel gas channel region 817 is about 600 ° C., and the temperature of the reforming reaction layer region 816 is It became about 520 degreeC. In the region 816 of the reforming reaction layer, a steam reforming reaction of methane occurred, and due to the endothermic effect, a rapid temperature drop was obtained in a narrow region.

  On the other hand, in the temperature distribution 820 of the cylindrical fuel cell according to the present embodiment, the temperature of the air channel region 828 is about 600 ° C., but the temperature of the fuel gas channel region 827 is about 570 ° C. The temperature of the quality reaction layer region 826 was about 560 ° C. Due to the action of the porous layer region 825 provided between the reforming reaction layer region 826 and the anode electrode region, the temperature distribution is uniform inside the fuel cell according to this embodiment. I understand.

  The temperature gradient in the cross section perpendicular to the length direction of the cylindrical fuel cell according to the prior art and the cylindrical fuel cell according to this example was examined. Regarding the fuel cell according to the prior art, the temperature distribution in the line segment 813 connecting the center point 811 of the cross section perpendicular to the length direction and the end point 812 of the air flow path region 818, and the fuel cell according to this embodiment The temperature distribution in the line segment 823 connecting the center point 821 of the cross section perpendicular to the length direction and the end point 822 of the air flow path region 828 was obtained. Hereinafter, the center point of the cross section perpendicular to the length direction of the fuel cell is simply referred to as “center point”.

  FIG. 9 is a graph showing the temperature distribution in a cross section perpendicular to the length direction of the fuel cell according to the prior art and the fuel cell according to the present example. FIG. 9 shows the relationship between the distance from the center point (that is, the position on the line segment 813 or the line segment 823) and the temperature. The temperature distribution 910 shows the temperature distribution on the line segment 813 of the cylindrical fuel cell according to the prior art, and the temperature distribution 920 shows the temperature distribution on the line segment 823 of the cylindrical fuel cell according to this embodiment. .

  From the graph of FIG. 9, it can be seen that there is a steep temperature gradient in the temperature distribution 910 from the position at a distance of 0.003 m from the center point 811 toward the position at 0.008 m. Since the radius of the fuel battery cell is 0.008 mm (diameter is 16 mm), the distance from the center point 811 at a high temperature of about 600 ° C. within the fuel battery cell is 0.003 m or less. It has been found that the distance from the center point 811 where a temperature gradient occurs is divided into an area of 0.003 m or more.

  On the other hand, when the temperature distribution 920 is seen, in the fuel cell according to the present embodiment, a gentle temperature gradient occurs at a position near the center point 821 of 0.002 m, but the temperature inside the fuel cell (center point) It can be seen that the temperature in the region where the distance from 821 is 0.008 m or less is substantially uniform. As shown in FIG. 6, the position where the distance from the center point 821 is 0.002 m is a position where the fuel gas flow path 607 and the reforming reaction layer 606 are in contact with each other. For this reason, at the position where the distance from the center point 821 is about 0.002 m, the temperature is lowered by the reforming reaction.

  It can also be seen that both temperature distribution 910 and temperature distribution 920 have temperature gradients in the region where the distance from the center point is 0.008 m or more. As for the temperature gradient in this region, the temperature distribution 920 of the fuel cell according to this embodiment is gentler than the temperature distribution 910 of the fuel cell according to the prior art. In addition, the area | region whose distance from a center point is 0.008 m or more is an area | region of an air flow path.

  From the graph of FIG. 9, the difference ΔT between the maximum temperature and the minimum temperature of the temperature distribution 910 is about 80 ° C. inside the fuel cell (the region where the distance from the center point is 0.008 m or less). The temperature difference ΔT is about 10 ° C. From this result, it was found that the fuel cell according to this example has a temperature difference ΔT of about one-eighth compared to the fuel cell according to the prior art.

The thermal stress σ can be obtained by Expression (4) using the Young's modulus E.
σ = E · εr = E · α · ΔT (4)
Here, εr is thermal strain and is represented by the product of the temperature difference ΔT and the linear expansion coefficient α.

  From Equation (4), if the Young's modulus E and the linear expansion coefficient α are constant, the thermal stress σ is proportional to the temperature difference ΔT. From this, the fuel cell according to this example has a difference ΔT between the maximum temperature and the minimum temperature inside the fuel cell that is about one-eighth compared with the fuel cell according to the prior art. It was found that it can be reduced to 1/8. Therefore, the fuel cell according to the present embodiment can prevent a decrease in durability due to thermal stress. In addition, local and rapid temperature drop of the electrode can be prevented, and performance degradation due to increase in electrode reaction overvoltage can be suppressed. Therefore, the fuel battery cell according to the present embodiment can reduce a decrease in power generation performance.

102, 202, 502, 602 ... cathode electrode,
103, 203, 503, 603 ... solid electrolyte,
104, 204, 504, 604 ... anode electrode,
105, 205, 605 ... porous layer,
106, 206, 306, 406, 506, 606, 1006, 1106 ... reforming reaction layer,
107, 207, 307, 407, 507, 607, 1007, 1107 ... fuel gas flow path,
200, 300, 400, 1000, 1100 ... fuel cell,
201, 501, 601 ... interconnector,
508, 608 ... air flow path,
509, 609 ... current collector plate,
810 ... temperature distribution of the fuel cell according to the prior art,
811, 821 ... the center point of the cross section,
812, 822 ... the end points of the region of the air flow path,
813, 823 ... line segment,
816, 826 ... the region of the reforming reaction layer,
817, 827 ... the region of the fuel gas flow path,
818, 828 ... the area of the air flow path,
820 ... Temperature distribution of the fuel cell according to the present embodiment,
825 ... the region of the porous layer,
910 ... Temperature distribution of the fuel cell according to the prior art,
920 ... temperature distribution of the fuel cell according to the present embodiment,
1008, 1009, 1010... The shape of the fuel gas channel.

Claims (8)

In a solid oxide fuel cell comprising: a cathode electrode; an anode electrode; a solid electrolyte disposed between the cathode electrode and the anode electrode; and a fuel gas flow path through which fuel gas flows.
A porous layer composed of a porous body is provided adjacent to the anode electrode;
A reforming reaction layer for reforming the fuel gas is provided adjacent to the porous layer;
The solid oxide fuel cell, wherein the fuel gas channel is provided adjacent to the reforming reaction layer. The solid oxide fuel cell according to claim 1, wherein
The solid electrolyte is cylindrical;
The cathode electrode is provided on the outer surface of the solid electrolyte,
The anode electrode is provided on the inner surface of the solid electrolyte,
The porous layer is provided inside the anode electrode,
The reforming reaction layer is provided inside the porous layer,
The fuel gas flow path is a solid oxide fuel cell provided inside the reforming reaction layer. The solid oxide fuel cell according to claim 1, wherein
The porous layer is composed of one selected from the group consisting of silicon nitride, silicon carbide, zirconia, alumina, mullite, and cordierite, and has a porosity of 30% or more and a thickness of 100 μm or more. A solid oxide fuel cell. The solid oxide fuel cell according to claim 2, wherein
The fuel gas flow path is a solid oxide fuel cell in which a cross section perpendicular to the length direction of the solid oxide fuel cell has a star shape. The solid oxide fuel cell according to claim 2, wherein
A plurality of the fuel gas flow paths;
Each of the plurality of fuel gas flow paths is surrounded by the reforming reaction layer, and is dispersed in the porous layer. The solid oxide fuel cell according to claim 2, wherein
The fuel gas flow path is a solid oxide fuel cell in which a cross-sectional area perpendicular to the length direction of the solid oxide fuel cell varies depending on a position in the length direction of the solid oxide fuel cell. The solid oxide fuel cell according to claim 4, wherein
The fuel gas flow path having a star-shaped cross section is a solid oxide fuel cell in which the star-shaped shape changes depending on the position of the solid oxide fuel cell in the length direction. The solid oxide fuel cell according to claim 5, wherein
The fuel gas flow path is a solid oxide fuel cell whose number varies depending on the position in the length direction of the solid oxide fuel cell.

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