Solid oxide fuel cell and method for controlling solid oxide fuel cell

Abstract

To shorten a warming-up time.SOLUTION: A solid oxide fuel battery is configured by laminating a plurality of fuel battery cells via a separator, each fuel battery cell being configured by an anode electrode layer, a cathode electrode layer, and a solid electrolyte layer held by the anode and cathode electrode layers. Between two adjacent fuel battery cells, a fuel passage for supplying a hydrocarbon-based fuel gas to the anode electrode layer and an air passage for supplying air to the cathode electrode layer are formed by the separator. The solid oxide fuel battery further comprises: a carbon generation part provided on the fuel passage, generating carbon from the fuel gas; and a burning catalyst provided on an inner peripheral surface of the separator, being capable of burning the fuel gas and storing the carbon generated by the carbon generation part.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a solid oxide fuel cell and a method for controlling a solid oxide fuel cell. [Background technology]

[0002] A solid oxide fuel cell stack, which is configured by stacking a plurality of fuel cells, has a high operating temperature, and therefore it is desirable to warm it up as quickly as possible when it is started up.

[0003] Patent Document 1 discloses a solid oxide fuel cell with a combustion catalyst on the anode side. In the fuel cell disclosed in Patent Document 1, a combustion catalyst is provided in the low-temperature part on the anode side. Then, city gas such as methane gas is used as fuel gas, and the fuel gas is combusted in the combustion catalyst to heat the low-temperature part. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2006-059614 A Summary of the Invention

[0005] According to the technology disclosed in Patent Document 1, warm-up is performed by supplying fuel gas at startup and burning it using a combustion catalyst, but because fuel gas is a gas and has a relatively low energy density, there was an issue that it took a long time to warm up the fuel cell.

[0006] The present invention has been made in consideration of the above-mentioned problems, and has an object to provide a solid oxide fuel cell that is capable of shortening the warm-up time.

[0007] According to one aspect of the present invention, a solid oxide fuel cell is constructed by stacking a plurality of fuel cells, each of which is composed of an anode layer, a cathode layer, and a solid electrolyte layer sandwiched between the anode layer and the cathode layer, with a separator interposed therebetween. Between two adjacent fuel cells, a fuel flow path that supplies a hydrocarbon fuel gas to the anode layer and an air flow path that supplies air to the cathode layer are formed by the separator. The solid oxide fuel cell further includes a carbon generator provided in the fuel flow path that generates carbon from the fuel gas, and a combustion catalyst provided on the inner circumferential surface of the separator that is capable of combusting the fuel gas and storing the carbon generated in the carbon generator. During start-up of the solid oxide fuel cell, the carbon generation unit generates carbon from the fuel gas supplied together with air to the fuel flow passage until the temperature of the anode off-gas exceeds a preset warm-up completion temperature, and the combustion catalyst burns the stored carbon with the fuel gas and air. When an instruction to stop power generation of the solid oxide fuel cell is received, the carbon generation unit generates carbon and the combustion catalyst stores the generated carbon in a state in which the amount of water vapor supplied to the fuel cell is reduced until the amount of carbon stored in the combustion catalyst reaches the amount required for the next start-up. do. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is an exploded perspective view of a fuel cell stack according to an embodiment of the present invention. [Diagram 2] FIG. 2 is an exploded perspective view of a cell unit. [Diagram 3] FIG. 3 is an exploded perspective view of the metal support cell assembly. [Figure 4] FIG. 4 is a partial cross-sectional view of the fuel cell stack. [Diagram 5] FIG. 5 is a cross-sectional view taken along line AA in FIG. [Figure 6] FIG. 6 is a system configuration diagram of a fuel cell system using a fuel cell stack. [Figure 7] FIG. 7 is a partial cross-sectional view of a fuel cell stack in which carbon deposition has occurred. [Figure 8] FIG. 8 is a cross-sectional view taken along line AA in FIG. [Figure 9] FIG. 9 is an enlarged cross-sectional view of a portion circled in FIG. 4, and is a schematic cross-sectional view illustrating the microstructure of the combustion catalyst. [Figure 10] FIG. 10 is an enlarged cross-sectional view of a portion enclosed by a circle C in FIG. 4, and is a schematic cross-sectional view illustrating the microstructure of the metal support. [Figure 11]FIG. 11 is a schematic diagram illustrating the state in which deposited carbon is stored. [Figure 12] FIG. 12 is a flowchart showing power generation control of the fuel cell system. [Figure 13] FIG. 13 is a partial cross-sectional view of a fuel cell stack according to a modified example. [Figure 14] FIG. 14 is a partial cross-sectional view of a fuel cell stack according to another modified example. [Figure 15] FIG. 15 is a schematic diagram illustrating a state in which deposited carbon is stored in another modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] 1 to 3 are diagrams illustrating the configuration of a fuel cell stack (solid oxide fuel cell) 100 according to an embodiment of the present invention. As shown in Fig. 1 and Fig. 2, the fuel cell stack 100 is composed of a plurality of cell units 1, and each cell unit 1 is composed of a metal support cell assembly 10 and a separator 20. Also, as shown in Fig. 3, the metal support cell assembly 10 is composed of a metal support cell 11 and a cell frame 12.

[0011] 1 is an exploded perspective view of a fuel cell stack 100. The fuel cell stack 100 is formed by stacking a plurality of plate-shaped cell units 1. Each cell unit 1 is provided near one longitudinal end with a fuel supply hole 11a through which fuel gas (anode gas) flows and an air supply hole 12a through which air (cathode gas) flows, and provided near the other end with a fuel exhaust hole 11b through which anode off-gas flows and an air exhaust hole 12b through which cathode off-gas flows.

[0012] FIG. 2 is an exploded perspective view of the cell unit 1. The cell unit 1 is constructed by stacking a metal support cell assembly (fuel cell) 10 and a separator 20. The metal support cell assembly 10 and the separator 20 are formed in a plate shape. A fuel supply hole 101a and an air supply hole 102a are provided near one end in the longitudinal direction of the metal support cell assembly 10, and a fuel exhaust hole 101b and an air exhaust hole 102b are provided near the other end. Similarly, a fuel supply hole 201a and an air supply hole 202a are provided near one end in the longitudinal direction of the separator 20, and a fuel exhaust hole 201b and an air exhaust hole 202b are provided near the other end. When the metal support cell assembly 10 and the separator 20 are stacked, the fuel supply hole 101a and the fuel supply hole 201a, and the air supply hole 102a and the air supply hole 202a overlap with each other, thereby forming the fuel supply hole 11a and the air supply hole 12a of the cell unit 1. Similarly, fuel exhaust hole 11b and air exhaust hole 12b of cell unit 1 are formed by overlapping fuel exhaust hole 101b and fuel exhaust hole 201b, and air exhaust hole 102b and air exhaust hole 202b, respectively.

[0013] In addition, a gas flow passage forming portion 21 is provided in the center of the separator 20. As shown in FIG. 2, the gas flow passage forming portion 21 is formed in a substantially linear shape such that the uneven shape extends in the longitudinal direction of the separator 20. When the separator 20 is stacked on the metal support cell assembly 10, a gas flow passage 40 (see FIGS. 4 and 5) partitioned by the gas flow passage forming portion 21 is formed between the upper surface of the metal support cell assembly 10 and the separator 20. In addition, the metal support cell assembly 10 of another cell unit 1 is stacked on the gas flow passage forming portion 21 of the separator 20. As a result, a gas flow passage 40 (see FIGS. 4 and 5) partitioned by the gas flow passage forming portion 21 is formed between the separator 20 and the metal support cell assembly 10 on the gas flow passage forming portion 21. As will be described later, the gas flow passage 40 formed between the separator 20 and the metal support cell assembly 10 stacked on the separator 20 constitutes a fuel flow passage 41. Further, the gas flow passage 40 formed between the upper surface of the metal support cell assembly 10 and the separator 20 constitutes an air flow passage 42 .

[0014] 3 is an exploded perspective view of the metal support cell assembly 10. The metal support cell assembly 10 has a metal support cell 11 and a cell frame 12 that surrounds the outer periphery of the metal support cell 11 and holds it.

[0015] The metal support cell 11 is formed by laminating an anode layer 50, a cathode layer 60, and a solid electrolyte layer 70 sandwiched between the anode layer 50 and the cathode layer 60 on a metal support 80, with the solid electrolyte layer 70 being made of a solid oxide. That is, the metal support cell assembly 10 is a fuel cell configured as a solid oxide fuel cell (SOFC) having the solid electrolyte layer 70. The anode layer 50, the cathode layer 60, the solid electrolyte layer 70, and the metal support 80 will be described in detail later.

[0016] The cell frame 12 is made of, for example, a plate-shaped metal, and has an opening 121 in the center in which the metal support cell 11 is placed. The solid electrolyte layer 70 of the metal support cell 11 is surface-bonded to the inner peripheral surface of the opening 121 of the cell frame 12 by sintering bonding or the like. In this way, the metal support cell 11 is held by the cell frame 12.

[0017] As described above, the fuel cell stack (solid oxide fuel cell) 100 is a stacked battery constructed by stacking cell units 1, each of which has a metal support cell assembly (fuel cell) 10 and a separator 20 stacked on top of each other. In this embodiment, the fuel cell stack 100 is intended to be mounted on a mobile vehicle such as an electric vehicle or a hybrid vehicle, but may also be used as a power source for various electrical devices.

[0018] Next, the gas flow in the fuel cell stack 100 will be described.

[0019] In the solid oxide fuel cell stack 100, air is used as the cathode gas, and hydrogen or a hydrocarbon fuel such as methane (CH4) is used as the anode gas. The type of fuel gas (anode gas) used in the fuel cell stack 100 is selected according to the fuel cell system to be constructed.

[0020] 1 are stacked, the fuel supply holes 11a and air supply holes 12a of each cell unit 1 overlap to form a flow path for fuel and a flow path for air (cathode gas). Also, the fuel exhaust holes 11b and air exhaust holes 12b of each cell unit 1 overlap to form a flow path for anode off-gas and a flow path for cathode off-gas.

[0021] A portion of the fuel gas flowing through the fuel supply hole 11a is supplied from the fuel supply hole 201a of the separator 20 to the gas flow path 40 (fuel flow path 41) defined by the gas flow path forming portion 21 of the separator 20 in each cell unit 1. The fuel supplied to the fuel flow path 41 is supplied from the fuel flow path 41 to the anode layer 50 of the metal support cell assembly 10 stacked on the separator 20. Anode off-gas after being used in the anode layer 50 is discharged to the flow path defined by the fuel discharge hole 11b. The space between the fuel supply hole 201a of the separator 20 and the fuel flow path 41 is sealed by a seal member (not shown) or the like so that only the fuel gas from the fuel supply hole 201a is supplied to the fuel flow path 41.

[0022] On the other hand, a part of the cathode gas flowing through the air supply hole 12a is supplied from the air supply hole 102a of the metal support cell assembly 10 to the gas flow path 40 (air flow path 42) partitioned and formed by the gas flow path forming portion 21 of the separator 20 in each cell unit 1. The cathode gas supplied to the air flow path 42 is supplied from the air flow path 42 to the cathode electrode layer 60 of the metal support cell assembly 10 on which the separator 20 is laminated. The cathode off-gas after being used in the cathode electrode layer 60 is discharged to the flow path formed by the air discharge hole 12b. The gap between the air supply hole 102a of the metal support cell assembly 10 and the air flow path 42 is sealed by a sealing member (not shown) or the like so that only the cathode gas from the air supply hole 102a is supplied to the air flow path 42.

[0023] As described above, the fuel gas flowing through the fuel supply hole 11a is supplied from the fuel supply hole 201a to the fuel flow path 41 defined by the separator 20, and the cathode gas flowing through the air supply hole 12a is supplied from the air supply hole 102a to the air flow path 42 defined by the separator 20.

[0024] Incidentally, since the solid oxide fuel cell stack 100 has a high operating temperature of about 600° C., it is preferable to warm it up quickly at startup. On the other hand, it is possible to warm it up quickly by using the heat of the combustion reaction by providing a combustion catalyst on the anode layer or the substrate (metal substrate) that supports the anode layer, but in this case, there is a risk that the anode layer 50 will deteriorate due to sintering or the like, or the substrate will deteriorate due to oxidation.

[0025] Therefore, in this embodiment, a reforming catalyst 91 that reforms the fuel is provided on the anode layer 50 and the metal support 80, while a combustion catalyst is provided on the inner circumferential surface of the separator 20 that forms the fuel flow path 41. As a result, even if combustion occurs due to the action of the combustion catalyst, the anode layer 50 and the metal support 80 are not directly combusted, so deterioration of the anode layer 50 and the metal support 80 is suppressed, and the radiant heat of the combustion in the separator 20 can warm up the fuel cell stack 100 in a short time.

[0026] 4 and 5 are partial cross-sectional views of a fuel cell stack 100 according to this embodiment, showing a gas flow path 40 and two adjacent fuel cell units 10 stacked above and below the gas flow path 40. Fig. 4 is a cross-sectional view seen from the front of the gas flow path 40, and Fig. 5 is a cross-sectional view taken along line AA in Fig. 4.

[0027] As described above, the cell unit 1 of the fuel cell stack 100 includes the fuel cell 10 and the separator 20. Also, as shown in Figures 4 and 5, the fuel cell 10 includes a solid electrolyte layer 70, a cathode layer 60 disposed on one surface of the solid electrolyte layer 70, an anode layer 50 disposed on the other surface of the solid electrolyte layer 70, and a metal support 80 provided to support the anode layer 50.

[0028] The solid electrolyte layer 70 is a thin film formed of an oxide having oxygen ion conductivity, and is sandwiched between the anode electrode layer 50 and the cathode electrode layer 60. As the oxide, for example, yttria-stabilized zirconia (YSZ), scandium-stabilized zirconia (SSZ), samarium-doped ceria (SDC), gadolinium-doped ceria (GDC), lanthanum strontium magnesium gallate (LSGM), etc. can be used.

[0029] The anode layer 50 is a plate-like member formed of a metal such as nickel (Ni) and an oxide such as yttria-stabilized zirconia (YSZ). The anode layer 50 is provided in contact with the lower surface of the solid electrolyte layer 70 and placed on a metal support 80. In the anode layer 50, an oxidation reaction occurs in which the oxide ions conducted through the solid electrolyte layer 70 oxidize the anode gas containing hydrogen and the like.

[0030] The cathode layer 60 is a plate-like member formed of, for example, lanthanum strontium cobalt composite oxide (LSC), lanthanum strontium cobalt iron oxide (LSCF), or the like, and is provided so as to be in contact with the upper surface of the solid electrolyte layer 70. In the cathode layer 60, a reduction reaction occurs that reduces oxygen in the cathode gas (air). The fuel cell 10 generates power based on the electrode reactions in the anode layer 50 and the cathode layer 60.

[0031] The metal support 80 is a porous plate-like member configured so as not to impede the conduction of the anode gas, and is provided to support the anode layer 50, functioning as a structural member for reinforcing the strength of the fuel cell 10. In this manner, the fuel cell 10 is configured as a so-called metal-support type fuel cell in which the anode layer 50, solid electrolyte layer 70, and cathode layer 60 are laminated on the metal support 80 as a support.

[0032] The separator 20 is disposed between two adjacent fuel cells 10, and forms a gas flow path 40 between the adjacent fuel cells 10. The gas flow path 40 includes a fuel flow path 41 through which fuel flows and an air flow path 42 through which air flows. The material forming the separator 20 is not particularly limited as long as it is an electrically conductive and thermally conductive material, but for example, an alloy or metal containing iron (Fe) or chromium (Cr) is used, and preferably, ferritic heat-resistant stainless steel is used. Examples of ferritic stainless steel include SUS430, SUS434, ZMG (registered trademark), and Crofer (registered trademark). The separator 20 may be an austenitic stainless steel. The separator 20 is a plate-shaped member formed by press-molding the above-mentioned electrically conductive and thermally conductive material, and is electrically connected to the fuel cell 10.

[0033] 4, the separator 20 includes a first contact portion 22 that contacts a metal support 80 (anode layer side) that supports the anode layer 50 of the fuel cell 10 stacked on the separator 20, and a second contact portion 23 that contacts a cathode layer 60 (cathode layer side) of the fuel cell 10 located below the separator 20. The first contact portion 22 and the second contact portion 23 are connected by a connecting portion 24.

[0034] The separator 20 is configured as an uneven member by connecting the first contact parts 22 and the second contact parts 23 arranged alternately (in order) in a predetermined direction (separator width direction) with the connecting parts 24. By having such an uneven structure, the separator 20 has a plurality of fuel flow paths 41 on one side surface and a plurality of air flow paths 42 on the other side surface. In FIG. 4, the connecting parts 24 are formed linearly and the fuel flow paths 41 are formed so that the cross-sectional area in the front direction of the flow path is trapezoidal, but this is not necessarily limited to this. For example, the connecting parts 24 may be formed in a curved shape and the fuel flow paths 41 may be configured so that the cross-sectional area of ​​the flow path is curved.

[0035] The first contact portion 22 and the second contact portion 23 of the separator 20 are formed as flat surfaces, with the first contact portion 22 contacting a metal support 80 of the fuel cell 10, and the second contact portion 23 contacting a cathode layer 60 of the fuel cell 10. The connecting portion 24 of the separator 20 is formed as a wall portion connecting an end of the first contact portion 22 and an end of the second contact portion 23. The space formed by the connecting portion 24, the second contact portion 23, and the metal support 80 becomes a fuel flow path 41 for supplying fuel to the anode layer 50. On the other hand, the space formed by the connecting portion 24, the first contact portion 22, and the cathode layer 60 becomes an air flow path 42 for supplying oxygen to the cathode layer 60.

[0036] In this manner, in the fuel cell stack 100, a fuel flow path 41 is formed between the separator 20 and the fuel cell 10 stacked on the separator 20, and an air flow path 42 is formed between the separator 20 and the fuel cell 10 located below the separator 20. The fuel flow path 41 contacts the lower surface of the metal support 80, and the air flow path 42 contacts the upper surface of the cathode layer 60. When the fuel cell stack 100 is in operation (power generation), fuel gas flows through the fuel flow path 41, and air containing oxygen (cathode gas) flows through the air flow path 42. The fuel gas is supplied from the fuel flow path 41 to the anode layer 50 via the metal support 80, and the cathode gas is supplied from the air flow path 42 to the cathode layer 60. The fuel flow path 41 and the metal support 80 may not be in direct contact with each other, but may be in contact with each other via a current collecting auxiliary layer that assists electrical contact and is formed, for example, by an expanded metal on a wire mesh.

[0037] Next, the arrangement of the catalyst will be described.

[0038] 4 and 5, a reforming catalyst 91 is provided on the anode layer 50 and the metal support 80 from a position above the upstream inlet (inlet) 411 of the fuel flow channel 41 to a position above the downstream outlet (outlet) 412 of the fuel flow channel 41. As a result, when a reformed fuel (hydrocarbon-based fuel) containing methane (CH4) is supplied from the fuel flow channel 41 to the anode layer side during operation (power generation) of the fuel cell stack 100, a reforming reaction of the hydrocarbon-based fuel is promoted by the reforming catalyst 91, and an anode gas containing hydrogen (H2) is generated.

[0039] The reforming catalyst 91 may be provided by any known method, for example, by impregnating the anode layer 50 with the catalyst or by applying the catalyst to the entire surface of the anode layer 50. The reforming catalyst 91 may be provided on a part of the metal support 80 in addition to the anode layer 50.

[0040] On the other hand, as shown in Figures 4 and 5, a combustion catalyst 92 is provided on the inner surface of the separator 20 that forms the fuel flow path 41, i.e., on the surfaces of the second abutment portion 23 and the connecting portion 24 facing the fuel flow path 41, from the upstream inlet 411 to the downstream outlet 412 of the fuel flow path 41.

[0041] Here, the operation of the fuel cell system 200 including the fuel cell stack 100 at startup and during operation (power generation) will be described with reference to FIG.

[0042] FIG. 6 is a schematic diagram of a fuel cell system 200 including a fuel cell stack 100. As shown in FIG.

[0043] A fuel supply path starting from a fuel tank 110 is connected to the fuel supply hole 11a of the fuel cell stack 100. A cathode supply path used to supply cathode gas (air) obtained from outside the fuel cell system 200 by a blower 120 is connected to the fuel supply path, and an anode ejector 111 is provided downstream of the connection point with the cathode supply path. An air ejector 112 is provided between the blower 120 and the fuel supply path and the cathode supply path. As described later, the cathode supply path connected to the fuel supply path is configured so that a part of the gas discharged from the heat exchanger 130 to the outside can be returned by operating a return ejector 160.

[0044] A hydrocarbon fuel gas is stored in the fuel tank 110, and the amount of fuel gas and cathode gas supplied to the fuel supply hole 11a of the fuel cell stack 100 can be controlled by operating the anode ejector 111. When the fuel cell stack 100 is started up, the anode ejector 111 and the air ejector 112 are opened to warm up the fuel cell stack 100, and the fuel gas supplied from the fuel supply hole 11a and oxygen contained in the cathode gas undergo a combustion reaction by a combustion catalyst 92 provided in the fuel flow path 41 in the fuel cell stack 100, thereby raising the temperature of the fuel cell stack 100. When the warm-up is completed, the air ejector 112 is closed and the supply of the cathode gas to the fuel flow path 41 is stopped.

[0045] The cathode supply passage that supplies the cathode gas taken in from the blower 120 branches off and is connected to the fuel supply passage as well as to a heat exchanger 130. The heat exchanger 130 is configured to be capable of heating by heat exchange with the adjacent exhaust combustor 140, and the heated cathode gas is supplied to the air supply hole 12a of the fuel cell stack 100.

[0046] The anode off-gas and cathode off-gas that have completed the reaction in the fuel cell stack 100 are discharged from the fuel exhaust hole 11b and the air exhaust hole 12b, respectively. A temperature sensor 150 is provided at the outlet of the fuel exhaust hole 11b, so that the temperature of the anode off-gas can be measured.

[0047] The anode off-gas flow passage connected to the fuel exhaust hole 11b and the cathode off-gas flow passage connected to the air exhaust hole 12b join together and are discharged to the exhaust combustor 140. The exhaust combustor 140 is provided with an exhaust catalyst, and mainly combusts unburned gas contained in the anode off-gas and discharges it to the outside. Since the exhaust combustor 140 is configured integrally with the heat exchanger 130, it is possible to heat the heat exchanger 130 using the combustion heat in the exhaust combustor 140.

[0048] In addition, the exhaust path that exhausts gas from the heat exchanger 130 to the outside of the fuel cell system 200 has a branch path, and the branch path is connected to a cathode supply path that is connected to a fuel supply path. This branch path is provided with a reflux ejector 160, and the amount of exhaust gas flowing into the fuel supply hole 11a can be controlled by operating the reflux ejector 160. Since the exhaust gas contains a water vapor component, the amount of water vapor supplied to the fuel cell stack 100 can be controlled by operating the reflux ejector 160.

[0049] The exhaust combustor 140 is configured to be able to receive fuel gas from the fuel tank 110 via the combustor ejector 113. At startup, the combustor ejector 113 is opened and fuel gas is supplied to the exhaust combustor 140. This causes a combustion reaction to proceed in the exhaust combustor 140, and the heated cathode gas flows into the air supply hole 12a due to heat exchange in the heat exchanger 130. In this way, the fuel cell stack 100 can be warmed up by the cathode gas heated by the heat generated in the exhaust combustor 140.

[0050] The controller 170 controls the operation of the fuel cell system 200 by acquiring the temperature from the temperature sensor 150, operating the anode ejector 111, the air ejector 112, the combustor ejector 113, and the return flow ejector 160, and controlling the amount of power generation by the fuel cell stack 100.

[0051] Here, when focusing on the exothermic reaction of the combustion catalyst 92 in the fuel cell stack 100 during warm-up, fuel gas and air containing oxygen are supplied to the fuel flow path 41, and a combustion reaction occurs by the combustion catalyst 92, and the fuel cell stack 100 is warmed up by the heat of the combustion reaction. Here, if the combustion catalyst 92 is provided on the anode layer 50 or the base material (metal support 80) supporting the anode layer 50, a combustion reaction occurs in the anode layer 50 or the metal support 80, so that there is a risk that the anode layer 50 may be deteriorated by sintering or the base material (metal support 80) may be oxidized and deteriorated. In contrast, in this embodiment, as shown in FIG. 4, the combustion catalyst 92 is provided on the inner circumferential surface (fuel flow path 41) of the separator 20, which has high heat resistance. Therefore, when fuel gas and air are supplied to the fuel flow path 41 during startup of the fuel cell stack 100, a combustion reaction occurs in the fuel flow path 41 by the combustion catalyst 92, but the separator 20 is not easily oxidized and deteriorated. Furthermore, the anode layer side is heated by radiant heat from the combustion reaction, warming up the fuel cell stack 100. In this way, since the anode layer side is heated by radiant heat rather than causing a direct combustion reaction in the anode layer 50 or the metal support 80, the fuel cell stack 100 can be warmed up quickly while suppressing deterioration of the anode layer 50 and the base material (metal support 80).

[0052] The combustion catalyst 92 may be provided by any known method, for example, by coating the inner circumferential surface of the separator 20 .

[0053] As described above, when the fuel cell stack 100 is started up, fuel gas and air (oxygen) are supplied to the fuel flow passage 41, but when the fuel cell stack 100 is operating (power generation), air (oxygen) is not supplied to the fuel flow passage 41, and reformable fuel gas (hydrocarbon fuel) is supplied instead. Thus, when the fuel cell stack 100 is operating (power generation), the amount of water vapor and oxygen contained in the air in the fuel flow passage 41 is small, and there is a risk that carbon components in the fuel gas will precipitate (caulk) on the reforming catalyst, particularly in the metal support 80.

[0054] Therefore, in this embodiment, a combustion catalyst 92 having a carbon storage ability that stores more carbon as the temperature increases is used as the combustion catalyst 92 provided on the anode electrode layer side. As a result, when the fuel cell stack 100 is in operation (power generation), carbon deposited on the combustion catalyst 92 heated by its own combustion heat is stored.

[0055] Fig. 7 is a diagram showing a state in which carbon deposition is performed in the configuration shown in Fig. 4. Also, Fig. 8 is a cross-sectional view taken along line AA in Fig. 7. As shown in these figures, at the start-up of the fuel cell stack 100, deposited solid carbon 93 is stored mainly on the second contact portion 23 of the combustion catalyst 92 that contacts the cathode layer 60.

[0056] On the other hand, when the fuel cell stack 100 is started up, the combustion catalyst 92 is at a lower temperature than when the fuel cell stack 100 is in operation, and therefore its carbon storage capacity is reduced, and as a result, the stored carbon is released from the combustion catalyst 92. The released carbon reacts with oxygen contained in the air supplied to the fuel flow path 41 at the time of startup and is burned. Here, since the released carbon is a solid, it has a higher energy density and a higher combustion reaction in the combustion catalyst 92 than the fuel gas, which is a gas supplied from the fuel tank 110. Therefore, by using the carbon stored in the combustion catalyst 92 for warming up, the warm-up time can be shortened.

[0057] FIG. 9 is an enlarged cross-sectional view of a portion enclosed by a circle B in FIG.

[0058] 9, the combustion catalyst 92 is formed by supporting catalyst particles 922 on a support 921. The catalyst particles 922 can be supported by, for example, spray coating or screen printing.

[0059] The catalytic fine particles 922 of the combustion catalyst 92 may be any known material, and may include, for example, palladium (Pd), or palladium (Pd) and any of nickel (Ni), rhodium (Rh), platinum (Pt), ruthenium (Ru), iridium (Ir), manganese (Mn), and cobalt (Co). Palladium (Pd) has a low activation energy of combustion reaction and is prone to combustion (high oxidation activity), and can have a high carbon storage capacity by forming a rough surface, so that the oxidation reaction is dominant in the combustion catalyst 92 containing palladium (Pd).

[0060] The support 921 of the combustion catalyst 92 is made of an oxide and may be any known oxide, for example, alumina (Al2O3), ceria (CeO2), zirconia (ZrO2), or a ceria-zirconia solid solution. The combustion catalyst 92 has supports 921 of various diameters relatively sparsely packed together, so that the surface area per unit area is relatively large and the surface is rough. Therefore, carbon can be stored between the supports 921.

[0061] As described above, the combustion catalyst 92 is provided on the inner circumferential surface of the separator 20 that forms the fuel flow path 41. Therefore, when air (oxygen) is supplied to the fuel flow path 41 at the start-up of the fuel cell stack 100, a combustion reaction occurs in the fuel flow path 41 due to the combustion catalyst 92. The fuel cell stack 100 is warmed up by the radiant heat of this combustion reaction, and the reforming catalyst 91 provided on the metal support 80 and the anode layer 50 is heated. In addition, since the combustion catalyst 92 has a carbon storage ability, it is able to adsorb carbon 93 and store carbon therein.

[0062] FIG. 10 is an enlarged cross-sectional view of a portion enclosed by a circle C in FIG. 4, and is a schematic cross-sectional view illustrating the microstructure of the metal support 80. As shown in FIG.

[0063] The metal support 80 is a metal member made of iron-chromium (Fe-Cr) steel, nickel (Ni), or the like, and is made of a sintered body of powder metal particles with a diameter of 1 micrometer or less. The metal support 80 is made of aligned fine particles of equal diameter, and is a metal body with a relatively small surface area per unit area and a dense and smooth surface. Therefore, it is active in the coking reaction and easily forms carbon compounds.

[0064] The detailed configuration of the reforming catalyst 91 is as follows. The reforming catalyst 91 is formed by supporting fine catalyst particles on a carrier. Methods for supporting the fine catalyst particles include, for example, impregnation, spray coating, and screen printing.

[0065] The catalyst particles of the reforming catalyst 91 may be any known material, and may include, for example, any of nickel (Ni), rhodium (Rh), platinum (Pt), ruthenium (Ru), iridium (Ir), manganese (Mn), and cobalt (Co).

[0066] The carrier of the reforming catalyst 91 is made of an oxide containing a substance having an oxygen storage capacity that stores more oxygen as the temperature increases. Specifically, the oxide contains any one of cerium (Ce), cerium (Ce) and zirconium (Zr), cerium (Ce), zirconium (Zr) and aluminum (Al), cerium (Ce), zirconium (Zr) and yttrium (Y), barium (Ba), cerium (Ce), zirconium (Zr) and yttrium (Y).

[0067] FIG. 11 is a schematic diagram illustrating carbon deposition on a metal support 80 and storage of carbon by a combustion catalyst 92.

[0068] When fuel cell stack 100 is started up, fuel gas (e.g., methane CH4) and air (oxygen) are supplied to fuel flow passage 41, and carbon (C) 93 is precipitated on metal support 80 having a dense surface. Carbon 93 precipitated on metal support 80 is generally in the form of fine particles, so it floats in fuel flow passage 41 and then comes into contact with combustion catalyst 92 below. Combustion catalyst 92 has a carbon storage capacity and fixes the floating carbon. In this way, carbon 93 is fixed on the surface of combustion catalyst 92, as shown in FIGS. 7 and 8.

[0069] Here, the fuel gas used in this embodiment is methane (CH4), and the reaction of the fuel gas in the fuel flow passage 41 differs depending on the amount of water vapor and oxygen contained in the air in the fuel flow passage 41.

[0070] Generally, during normal operation, air is not supplied to the fuel flow path 41 via the blower 120, the oxygen ratio is relatively low, and the amount of water vapor contained in the fuel gas is relatively large, so that steam reforming and water gas shift are carried out as follows.

[0071] (Steam reforming) CH4+H2O→3H2+CO (Water-gas shift) CO+H2O→H2+CO2

[0072] On the other hand, when the amount of water vapor is small, specifically when the S (Steam:water) / C (Carbon:CH4) ratio, which indicates the molar ratio of water vapor to carbon, is about 1, carbon deposition will occur as follows:

[0073] (Carbon deposition) CH4+H2O→C+2H2

[0074] Furthermore, when there is almost no water vapor, specifically when the S / C ratio is close to 0, the POx reaction proceeds as follows, generating reducing gas (CO). The generation of such reducing gas can suppress the oxidation of the anode.

[0075] (POx reforming) CH4+1 / 2O2→2H2+CO

[0076] Since the exhaust gas discharged to the outside through the exhaust combustor 140 contains water vapor, when the amount of water vapor contained in the fuel gas supplied to the fuel flow path 41 is small, the return ejector 160 is operated to change the amount of water vapor returned to the fuel supply path, thereby controlling the S / C ratio and causing carbon deposition or POx reforming.

[0077] FIG. 12 is a diagram showing power generation control of a fuel cell system 200 including the fuel cell stack 100 of this embodiment.

[0078] In step S1, the controller 170 starts the blower 120 and opens the anode ejector 111, the air ejector 112, and the combustor ejector 113 to start a warm-up process in which the fuel gas is combusted by the combustion catalyst 92. In addition, carbon that was deposited in the processes of steps S8 and S9 described below at the previous startup has been stored in the combustion catalyst 92. Therefore, in the combustion catalyst 92, in addition to the fuel gas that is supplied, carbon 93 stored in the combustion catalyst 92 is combusted, thereby warming up the fuel cell stack 100.

[0079] In step S2, the controller 170 determines whether the temperature of the anode off-gas acquired by the temperature sensor 150 exceeds the POx reaction start temperature. If the acquired temperature is below the POx reforming start temperature (S2: No), the controller 170 returns to the process of step S1 and continues the warm-up control. On the other hand, if the acquired temperature exceeds the POx reforming start temperature (S2: Yes), the controller 170 next performs the process of step S3.

[0080] In step S3, the controller 170 closes the air ejector 112 and reduces the amount of water vapor returned to the fuel supply passage to lower the S / C ratio (to about 0) so that POx reforming can be performed. This allows the POx reforming of the supplied fuel gas to proceed.

[0081] Here, the POx reforming start temperature is, for example, about 500°C, which is the temperature at which the combustion catalyst 92 provided in the fuel flow path 41 is easily oxidized. Therefore, when the temperature of the fuel cell stack 100 reaches the POx reforming start temperature, the POx reaction is advanced to fill the fuel flow path 41 with reducing gas (CO) to create a reducing atmosphere, thereby suppressing oxidation of the combustion catalyst 92 and the like.

[0082] Then, in step S4, the controller 170 determines whether the temperature of the anode off-gas acquired by the temperature sensor 150 exceeds the warm-up completion temperature. If the acquired temperature is below the warm-up completion temperature (S4: No), the controller 170 returns to the process of step S3 and continues the warm-up control. On the other hand, if the acquired temperature exceeds the warm-up completion temperature (S4: Yes), the controller 170 next performs the process of step S5.

[0083] In step S5, the controller 170 opens the reflux ejector 160 and increases the amount of water vapor returned to the fuel supply path so that steam reforming and water gas shift are performed on the fuel gas, thereby increasing the S / C ratio (to 2 or more). In this manner, the power generation process in the fuel cell stack 100 is started. Note that if the amount of water vapor in the fuel gas is sufficient, the reflux ejector 160 does not need to be operated.

[0084] In step S6, the controller 170 determines whether or not it has received a stop command for the fuel cell stack 100. If a stop command has been received (S6: Yes), the controller 170 then performs the process of step S7. If a stop command has not been received (S6: No), the controller 170 returns to the process of step S5 and continues power generation control.

[0085] In step S7, the controller 170 controls the recirculation ejector 160 in a direction to close so that carbon deposition occurs in the fuel gas, thereby reducing the amount of water vapor recirculated to the fuel supply path and reducing the S / C ratio (to about 1). In this way, in step S8, carbon deposition progresses, and the deposited carbon is stored in the combustion catalyst 92. Note that, if the recirculation ejector 160 is not opened in step S5, the amount of water vapor may be increased by opening the air ejector 112 to take in air.

[0086] In step S9, the controller 170 judges whether or not carbon deposition has been performed for a predetermined time. If the predetermined time or more has not elapsed (S9: No), the controller 170 returns to the process of step S8 and continues power generation control. On the other hand, if the predetermined time or more has elapsed since carbon deposition (S9: Yes), the controller 170 next performs the process of step S10.

[0087] The predetermined time is the time required for the amount of deposited carbon to exceed the amount required during the startup control of step S1 the next time the fuel cell system 200 operates. By doing so, the next time the fuel cell system 200 is started up, the carbon held in the combustion catalyst 92 can be used in the startup control (warm-up control) of step S1, thereby shortening the warm-up time.

[0088] In step S9, the controller 170 determines that after carbon deposition has been carried out for a predetermined period of time, the amount of carbon required for the next startup of the fuel cell system 200 is retained in the combustion catalyst 92, and completely shuts down the system.

[0089] In this manner, before the fuel cell system 200 is completely shut down, the S / C is controlled to about 1, promoting carbon deposition in the separator 20 and storing the deposited carbon in the combustion catalyst 92. As a result, when the fuel cell system 200 is restarted after a complete shutdown, warm-up control is performed using the high-energy-density carbon held in the combustion catalyst 92, thereby making it possible to reduce the warm-up time.

[0090] In this embodiment, as shown in Fig. 6, a part of the gas discharged from the exhaust combustor 140 is recirculated through the recirculation ejector 160, and the amount of water vapor (S / C ratio) supplied to the fuel supply hole 11a is controlled by operating the recirculation ejector 160, but this is not limiting. A water tank may be provided near the blower 120 without recirculating the gas discharged from the exhaust combustor 140. In addition, since the air taken in through the blower 120 contains water vapor, the amount of water vapor may be controlled by operating the air ejector 112.

[0091] According to this embodiment, the following effects can be obtained.

[0092] In the solid oxide fuel cell stack 100 of this embodiment, a plurality of fuel cells 10 each composed of an anode layer 50, a cathode layer 60, and a solid electrolyte layer 70 sandwiched between the anode layer 50 and the cathode layer 60 are stacked with separators 20 interposed therebetween, and a fuel flow path 41 for supplying a fuel gas composed of a hydrocarbon to the anode layer 50 is formed between two adjacent fuel cells 10 by the separators 20. The fuel flow path 41 has a carbon generation section (metal support 80) that generates carbon from the fuel gas, and a combustion catalyst 92 that is provided on the inner circumferential surface of the separator 20, is capable of combusting the fuel gas, and is capable of storing the carbon generated in the carbon generation section.

[0093] Here, there is a risk that the carbon generated (deposited) by the carbon generation unit will be discharged to the outside of the fuel cell stack 100 together with the anode off-gas. However, in this embodiment, by providing the combustion catalyst 92, it is possible to increase the amount of carbon generated by the carbon generation unit (metal support 80) stored in the fuel cell stack 100. Since the deposited carbon is a solid and has a high energy density, by burning the carbon stored in the combustion catalyst 92 in the warm-up control at the next startup, it is possible to reduce the warm-up time compared to the case where only the fuel gas is burned in the combustion catalyst 92.

[0094] Furthermore, both the carbon generation section (metal support 80) and the combustion catalyst 92 having carbon storage capacity are provided in the fuel flow passage 41. Therefore, the carbon generated in the carbon generation section does not remain suspended in the fuel flow passage 41 for a long time, but reaches and is stored in the combustion catalyst 92, thereby improving the carbon storage efficiency.

[0095] Furthermore, the combustion catalyst 92 is not provided on the inner circumferential surface of the metal support 80. Therefore, the anode layer 50 and the metal support 80 are not directly combusted, and deterioration of the anode layer 50 and the base material (metal support 80) can be suppressed.

[0096] According to the fuel cell stack 100 of this embodiment, the combustion catalyst 92 has a larger surface area per unit area and a rougher surface than the carbon generation section (metal support 80). By providing the combustion catalyst 92 having such a configuration, the surface available for storing carbon becomes larger, and therefore the carbon storage capacity is improved, and the wall resistance of the fuel flow path 41 becomes larger. As a result, the deposited carbon is less likely to be discharged to the outside of the fuel cell stack 100, and therefore the amount of carbon stored can be increased. Furthermore, by reducing the flow path cross-sectional area of ​​the fuel flow path 41, turbulence is more likely to occur in the fuel flow path 41, and therefore the carbon storage capacity can be improved.

[0097] According to the fuel cell stack 100 of this embodiment, the combustion catalyst 92 is made of palladium (Pd). Palladium has a property of having low activation energy of a combustion reaction and being easily combusted (high oxidation activity), and by forming a rough surface (large surface area per unit area), the carbon storage capacity can be increased. As a result, by using palladium for the combustion catalyst 92, it is possible to store carbon generated in the carbon generation section (metal support 80) and to easily combust the stored carbon.

[0098] According to the fuel cell stack 100 of this embodiment, the carbon generation portion is a part of the metal support 80. The metal support 80 is a sintered body in which metal particles are densely aligned, and therefore carbon precipitation from carbon compounds is likely to occur. By using such a metal support 80 for carbon precipitation in addition to holding the anode layer 50, the cathode layer 60, and the solid electrolyte layer 70, it becomes unnecessary to add a new member that promotes carbon precipitation, and therefore the configuration of the fuel cell stack 100 can be simplified.

[0099] In the solid oxide fuel cell stack 100 of this embodiment, the separator 20 is made of stainless steel. Since stainless steel has high heat resistance, deterioration caused by the combustion of fuel gas or carbon by the combustion catalyst 92 can be suppressed.

[0100] According to the control method for the solid oxide fuel cell stack 100 of this embodiment, when a command to stop the fuel cell stack 100 is received, the amount of water vapor supplied to the fuel cell 10 is reduced to generate carbon in the carbon generation section (metal support 80). Here, carbon deposition can be caused by reducing the amount of water vapor so that the S / C ratio (molar ratio of water vapor amount to carbon amount) is 1 or less. Then, when a predetermined time has elapsed after the amount of water vapor is reduced, power generation of the fuel cell stack 100 is stopped. Since the precipitated carbon is fixed and has a high energy density, the warm-up time can be reduced compared to when only fuel gas is used in the warm-up control at the next startup.

[0101] According to the control method for the solid oxide fuel cell stack 100 of this embodiment, the fuel cell stack 100 includes a combustion catalyst 92 capable of storing carbon generated in the carbon generation section (metal support 80). By including the combustion catalyst 92 in this manner, the carbon generated by the carbon generation section can be efficiently stored in the fuel cell stack 100.

[0102] (First Modification) In this embodiment, the combustion catalyst 92 is provided on the inner circumferential surface of the separator 20 from the inlet 411 to the outlet 412 of the fuel flow channel 41, but is not limited to this. The position and distance at which the combustion catalyst 92 is provided can be determined appropriately.

[0103] 13, in a modified example, in a fuel flow passage 41, the metal support 80 is provided from the end of the inlet 411 on the upstream side in the flow direction of the fuel flow passage 41, while the combustion catalyst 92 is provided on the inner circumferential surface of the separator 20 from a position a predetermined distance downstream from the inlet 411. The upstream side here means the side upstream of the center of the fuel flow passage 41 in the flow direction.

[0104] According to this modification, carbon generated in the metal support 80 moves in the flow direction of the fuel flow passage 41 and is then stored in the combustion catalyst 92, so that the generated carbon can be sufficiently stored even if the metal support 80 is provided at a location a predetermined distance away from the end of the inlet 411. At the same time, by not providing the combustion catalyst 92 from the end of the inlet 411, the installation area of ​​the combustion catalyst 92 can be reduced, and therefore the manufacturing cost of the fuel cell stack 100 can be reduced.

[0105] 14, in the cross-sectional view of the gas flow path 40 along the flow direction, in the fuel flow path 41, regions where the combustion catalyst 92 is provided in the flow direction of the fuel flow path 41 and regions where the combustion catalyst 92 is not provided may be provided alternately on the separator 20. In other words, the combustion catalyst 92 is provided discretely in the flow direction of the fuel flow path 41.

[0106] FIG. 15 is a schematic diagram for explaining carbon deposition in the separator 20 and absorption of carbon by the combustion catalyst 92 when the combustion catalyst 92 is provided as in FIG.

[0107] The separator 20 is made of stainless steel with a smooth surface, and has a property that facilitates carbon deposition similar to that of the metal support 80, and corresponds to a carbon generation portion. Here, the combustion catalyst 92 is provided discretely on the separator 20, so carbon deposition occurs in the region of the separator 20 where the combustion catalyst 92 is not provided. The carbon deposited in this manner is stored in the combustion catalyst 92 located downstream of the region where carbon deposition occurs.

[0108] By configuring in this manner as in the other modified example, the generated carbon can be efficiently stored in the combustion catalyst 92. At the same time, by providing the combustion catalyst 92 discretely in the flow direction, the installation area of ​​the combustion catalyst 92 can be reduced, thereby reducing the manufacturing cost of the fuel cell stack 100.

[0109] In the present embodiment and the modified example, the separator 20 and the metal support 80 constituting the wall surface of the fuel flow passage 41 are used as the carbon generation portion, but the present invention is not limited to this. Carbon deposition may be promoted by disposing a member having a smooth surface and active in the coking reaction in the fuel flow passage 41.

[0110] Although the embodiments of the present invention have been described above, the above-mentioned embodiments merely show some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above-mentioned embodiments. [Explanation of symbols]

[0111] 1 Cell Unit 10 Fuel cell (metal support cell assembly) 11 Metal Support Cell 12 Cell Frame 20 Separator 40 Gas flow path 41 Fuel flow passage 42 Air flow path 50 Anode layer 60 Cathode layer 70 Solid electrolyte layer 80 Metal support 91 Reforming catalyst 92 Combustion Catalyst 93 Carbon 100 Fuel Cell Stack 120 Blower 130 Heat exchanger 140 Exhaust Combustor 200 Fuel Cell System

Claims

1. A solid oxide fuel cell comprising: a plurality of fuel cell units each including an anode layer, a cathode layer, and a solid electrolyte layer sandwiched between the anode layer and the cathode layer, stacked with a separator interposed therebetween; and a fuel flow path for supplying a hydrocarbon fuel gas to the anode layer and an air flow path for supplying air to the cathode layer are formed by the separator between two adjacent fuel cell units, a carbon generating unit provided in the fuel flow path and generating carbon from the fuel gas; a combustion catalyst provided on an inner circumferential surface of the separator, the combustion catalyst being capable of combusting the fuel gas and storing the carbon generated in the carbon generating section, During start-up of the solid oxide fuel cell, the carbon generating unit generates the carbon from the fuel gas supplied together with the air to the fuel flow path until the temperature of the anode off-gas exceeds a preset warm-up completion temperature, and the combustion catalyst combusts the fuel gas, the air, and the stored carbon, When an instruction to stop power generation of the solid oxide fuel cell is received, the carbon generation unit generates the carbon in a state in which the amount of water vapor supplied to the fuel cell is reduced until the amount of carbon stored in the combustion catalyst reaches the amount required for the next startup, and the generated carbon is stored in the combustion catalyst.

2. 2. The solid oxide fuel cell according to claim 1, The combustion catalyst has a rougher surface than the carbon generating portion. Solid oxide fuel cell.

3. 3. The solid oxide fuel cell according to claim 2, The combustion catalyst is composed of palladium. Solid oxide fuel cell.

4. 4. The solid oxide fuel cell according to claim 1, The separator is made of stainless steel. Solid oxide fuel cell.

5. The solid oxide fuel cell according to claim 4, The carbon generating portion is a metal support that holds the anode layer. Solid oxide fuel cell.

6. 6. A solid oxide fuel cell according to claim 1, A solid oxide fuel cell, wherein an end of the combustion catalyst is provided downstream of an end of the carbon production section at an upstream end of the fuel flow channel.

7. 5. The solid oxide fuel cell according to claim 1, the combustion catalyst is provided discretely on an inner circumferential surface of the separator along a flow direction of the fuel flow channel, The carbon generation portion is a portion of the separator where the combustion catalyst is not provided. Solid oxide fuel cell.

8. a fuel cell comprising: a carbon generator provided in the fuel flow path and capable of generating carbon from the fuel gas; and a combustion catalyst provided on an inner circumferential surface of the separator and capable of combusting the fuel gas and storing the carbon generated in the carbon generator, the carbon generator comprising: a plurality of fuel cell units each including an anode layer, a cathode layer, and a solid electrolyte layer sandwiched between the anode layer and the cathode layer, stacked with a separator interposed therebetween; a fuel flow path for supplying a hydrocarbon fuel gas to the anode layer and an air flow path for supplying air to the cathode layer formed by the separator between two adjacent fuel cell units; At the start-up of the solid oxide fuel cell, the fuel gas and the air are supplied to the fuel flow path, and a warm-up process is performed in which the fuel gas and the carbon stored in the combustion catalyst are combusted in the combustion catalyst until a temperature of an anode off-gas exceeds a preset warm-up completion temperature; When an instruction to stop power generation of the solid oxide fuel cell is received, the amount of water vapor supplied to the fuel cell is reduced to generate the carbon in the carbon generating unit; A control method for a solid oxide fuel cell, comprising: stopping the supply of the fuel gas to the solid oxide fuel cell when the amount of carbon stored in the combustion catalyst reaches the amount required for the next startup after reducing the amount of water vapor.

9. A method for controlling a solid oxide fuel cell according to claim 8, comprising the steps of: A control method for a solid oxide fuel cell, when an instruction to stop power generation of the solid oxide fuel cell is received, the carbon is generated in the carbon generation unit by reducing the molar amount of water in the water vapor supplied to the fuel cell until it becomes smaller than the molar amount of carbon in the fuel gas.

10. A method for controlling a solid oxide fuel cell according to claim 8 or 9, comprising the steps of: A control method for a solid oxide fuel cell, when an instruction to stop power generation of the solid oxide fuel cell is received, the amount of water vapor supplied to the fuel cell is reduced, thereby generating carbon in the carbon generation unit, and storing the carbon generated in the carbon generation unit in the combustion catalyst.

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