Solid Oxide Fuel Cell

Abstract

To provide a solid oxide fuel cell capable of inhibiting a temperature distribution of a SOFC cell from being uneven while raising a temperature of the SOFC in a short time.SOLUTION: A solid oxide fuel cell 100 is provided which includes a plurality of SOFC cells 10 that each are obtained by laminating on a metal support body 50 an anode electrode layer 40, a cathode electrode layer 30, and a solid electrolyte layer 20 sandwiched between the anode electrode layer 40 and the cathode electrode layer 30, the SOFC cells 10 laminated via a separator 60. The separator 60 forms a fuel passage 65 for supplying fuel to the anode electrode layer 40 between two of the SOFC cells 10 adjacent to each other. A heat-resistant metal material 80 is disposed on the fuel passage 65's bottom surface on an entrance side. A partial oxidation catalyst 70 is applied on surfaces of the separator 60 and the heat-resistant metal material 80, the surfaces facing the anode electrode layer 40.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] In a fuel cell system, the heat generated when fuel is burned in a combustor heats air, and the heated air is then supplied to the fuel cell stack to warm it up to its operating temperature. However, this method requires the heat generated by combustion to be exchanged in a heat exchanger, and heat is dissipated as the heated air travels from the heat exchanger to the fuel cell stack. This means that warming up takes time, particularly in the case of solid oxide fuel cells (SOFCs), which have high operating temperatures, resulting in long startup times.

[0003] Patent Document 1 discloses an SOFC stack in which a catalyst layer having partial oxidation reforming capability and steam reforming capability is provided between the SOFC cells. In this SOFC stack, when the SOFC starts up, a partial oxidation reforming reaction is caused to proceed in the catalyst layer provided between the SOFC cells, and the heat generated by the partial oxidation reforming reaction directly heats the SOFC stack. This shortens the start-up time of the SOFC stack. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-200709 Summary of the Invention [Problem to be solved by the invention]

[0005] In the SOFC stack described in Patent Document 1, when a reforming feedstock and an oxygen-containing gas are actually supplied to the catalyst layer to cause a partial oxidation reforming reaction, a combustion reaction tends to occur near the inlet of the catalyst layer, causing localized high temperatures and uneven temperature distribution. If the temperature distribution of the SOFC cells becomes uneven like this, there is a risk that the output performance of the SOFC stack will decrease.

[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 can raise the temperature of an SOFC in a short time while suppressing uneven temperature distribution in the SOFC cell. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a solid oxide fuel cell including a plurality of fuel cell units, each of which is formed by stacking an anode layer, a cathode layer, and a solid electrolyte layer sandwiched between the anode layer and the cathode layer on a metal support, with these fuel cell units stacked with a separator interposed therebetween. The separator forms a fuel flow path between two adjacent fuel cell units for supplying fuel to the anode layer, and a heat-resistant metal material is disposed on the bottom surface on the inlet side of the fuel flow path, and a partial oxidation catalyst is applied to the separator and the heat-resistant metal material on the surfaces facing the anode layer. [Effects of the Invention]

[0008] According to the present invention, a heat-resistant metal material is disposed on the bottom surface of the inlet side of the fuel flow channel, and a partial oxidation catalyst is applied to the separator forming the fuel flow channel and the surface of the heat-resistant metal material facing the anode layer. Therefore, even if a partial oxidation reaction occurs inside the SOFC (fuel flow channel), the heat-resistant metal material disposed on the inlet side can prevent the inlet side of the fuel flow channel from becoming locally hot. Therefore, it is possible to heat the SOFC in a short time while preventing the temperature distribution of the SOFC cell from becoming uneven. [Brief explanation of the drawings]

[0009] [Figure 1]FIG. 1 is a schematic diagram of a solid oxide fuel cell stack according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating the supply of fuel gas and oxygen-containing gas when the fuel cell stack is started up. [Figure 3] FIG. 3 is an enlarged cross-sectional view of the circled portion in FIG. 1, and is a schematic cross-sectional view illustrating the microstructure of the reforming catalyst. [Figure 4] FIG. 4 is a partial cross-sectional view of the fuel cell stack as seen from the side of the anode gas flow channel. [Figure 5] FIG. 5 is a cross-sectional view taken along line BB in FIG. [Figure 6] FIG. 6 is a cross-sectional view taken along line AA in FIG. [Figure 7] FIG. 7 is a graph showing the difference in temperature in the anode gas flow channel depending on whether or not a heat-resistant metal material is present. [Figure 8] FIG. 8 is a cross-sectional view of an anode gas flow channel according to a modification of the first embodiment, as viewed from the front of the flow channel. [Figure 9] FIG. 9 is a partial cross-sectional view of a fuel cell stack according to another modification of the first embodiment. [Figure 10] FIG. 10 is a schematic diagram of a solid oxide fuel cell stack according to the second embodiment. [Figure 11] FIG. 11 is a cross-sectional view taken along line CC in FIG. [Figure 12] FIG. 12 is a partial cross-sectional view of a fuel cell stack according to a modification of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0011] (First embodiment) FIG. 1 is a schematic diagram of a solid oxide fuel cell stack 100 according to a first embodiment of the present invention, showing a cross section of two adjacent fuel cells 10. As shown in FIG.

[0012] A fuel cell stack (fuel cell) 100 is a stacked battery constructed by sequentially stacking solid oxide fuel cell cells (hereinafter referred to as fuel cell cells) 10 as unit cells and separators 60. FIG. 1 shows a cross section of two adjacent fuel cell cells 10 among a plurality of stacked fuel cell cells 10 and the separator 60 provided between them. 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.

[0013] The solid oxide fuel cell stack 100 has a high operating temperature of approximately 600°C. In the solid oxide fuel cell stack 100, air is used as the cathode gas, and hydrogen or a hydrocarbon fuel such as methane is used as the anode gas. The fuel gases such as the anode gas used in the fuel cell stack 100 are selected depending on the fuel cell system to be constructed.

[0014] The fuel cell 10 includes a solid electrolyte layer 20, a cathode layer 30 disposed on one side of the solid electrolyte layer 20, an anode layer 40 disposed on the other side of the solid electrolyte layer 20, and a metal support 50 provided to support the anode layer 40.

[0015] The solid electrolyte layer 20 is a thin film made of an oxide with oxygen ion conductivity, and is sandwiched between the anode electrode layer 40 and the cathode electrode layer 30. Examples of the oxide that can be used include yttria-stabilized zirconia (YSZ), scandium-stabilized zirconia (SSZ), samarium-doped ceria (SDC), gadolinium-doped ceria (GDC), and lanthanum strontium magnesium gallate (LSGM).

[0016] The cathode layer 30 is a plate-like member made 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 20. In the cathode layer 30, a reduction reaction occurs that reduces oxygen in the cathode gas (air). A current collector having a current collecting function may be pressure-bonded to the surface of the cathode layer 30 opposite to the side in contact with the solid electrolyte layer 20.

[0017] The anode layer 40 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 40 is provided so as to contact the lower surface of the solid electrolyte layer 20 and is placed on a metal support 50. In the anode layer 40, an oxidation reaction occurs in which oxide ions that have been conducted through the solid electrolyte layer 20 oxidize anode gas containing hydrogen and the like. The fuel cell 10 generates power based on electrode reactions in the cathode layer 30 and the anode layer 40. A current collector having a current collecting function may be pressure-bonded to the surface of the anode layer 40 opposite the side that contacts the solid electrolyte layer 20, and interposed between the anode layer 40 and the metal support 50.

[0018] The metal support 50 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 40, functioning as a structural member for reinforcing the strength of the fuel cell 10. In this way, the fuel cell 10 is configured as a so-called metal-supported fuel cell, in which the anode layer 40, solid electrolyte layer 20, and cathode layer 30 are stacked on the metal support 50 as a support.

[0019] The fuel cell stack 100 is constructed by stacking the above-described fuel cell units 10, with plate-shaped separators 60 provided between adjacent fuel cell units 10. The material forming the separators 60 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 ferritic stainless steel is preferably used. Examples of ferritic stainless steel include SUS430, SUS434, ZMG (registered trademark), and Crofer (registered trademark). The separators 60 are plate-shaped members formed by press-molding the above-described electrically conductive and thermally conductive material, and are electrically connected to the fuel cell units 10. As will be described later, the separators 60 form fuel flow paths 65 and transfer heat generated by partial oxidation reactions in the fuel flow paths 65 to the fuel cell units 10.

[0020] The separator 60 has a first abutment portion 61 that abuts against the metal support 50 (anode layer side) that supports the anode layer 40 of one of the two adjacent fuel cell cells 10, a second abutment portion 62 that abuts against the cathode layer 30 (cathode layer side) of the other of the two adjacent fuel cell cells 10, and a connecting portion 63 that connects the first abutment portion 61 and the second abutment portion 62.

[0021] The separator 60 is configured as an uneven member by connecting first contact portions 61 and second contact portions 62, which are arranged alternately (in order) in a predetermined direction (separator width direction), with connecting portions 63. Due to this uneven structure, the separator 60 has a plurality of cathode gas flow paths (air flow paths) 64 on one side and a plurality of anode gas flow paths (fuel flow paths) 65 on the other side. In FIG. 1, the connecting portions 63 are formed linearly and the anode gas flow paths 65 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 portions 63 may be formed in a curved shape, and the anode gas flow paths 65 may be configured so that the cross-sectional area of ​​the flow path is curved. In other words, the uneven shape referred to here also includes a curved shape. In this way, since the separator 60 has an uneven (including curved) structure, even if the metal support 50 or the like is displaced in a solid oxide fuel cell stack 100 with a high operating temperature, the separator 60 can follow the displacement.

[0022] The first contact portion 61 of the separator 60 is formed as a flat surface and contacts the metal support 50 of the fuel cell 10. The separator 60 is fixed to the metal support 50, for example, by welding a part of the first contact portion 61 to a part of the metal support 50.

[0023] The second contact portion 62 of the separator 60 is formed as a flat surface and contacts the cathode layer 30 of the fuel cell 10. The separator 60 is fixed to the cathode layer 30, for example, by welding a part of the second contact portion 62 to a part of the cathode layer 30.

[0024] The connecting portion 63 of the separator 60 is formed as a wall portion connecting an end of the first contact portion 61 and an end of the second contact portion 62. The space formed by the connecting portion 63, the second contact portion 62, and the metal support 50 serves as an anode gas flow path 65 for supplying fuel to the anode layer 40. On the other hand, the space formed by the connecting portion 63, the first contact portion 61, and the cathode layer 30 serves as a cathode gas flow path 64 for supplying oxygen to the cathode layer 30.

[0025] A partial oxidation catalyst 70 that promotes the partial oxidation reaction is applied to the surface of the separator 60 that faces the anode layer 40 across the metal support 50 (hereinafter referred to as the surface facing the anode layer 40).

[0026] FIG. 2 is a schematic diagram illustrating the supply of fuel gas and oxygen-containing gas when the fuel cell stack 100 is started up.

[0027] As shown in FIG. 2, the pipe for supplying the cathode gas (oxygen-containing gas) is divided so that the oxygen-containing gas can be supplied to both the cathode gas flow path 64 and the anode gas flow path 65. The amounts and ratios of the oxygen-containing gas supplied to the cathode gas flow path 64 and the anode gas flow path 65 are adjusted by a control unit or the like (not shown) of the fuel cell system. During normal operation after warming up the fuel cell stack 100, the reformed anode gas is supplied to the anode gas flow path 65, and the cathode gas (oxygen-containing gas) is supplied to the cathode gas flow path 64. On the other hand, during startup of the fuel cell stack 100, a reforming feedstock (hydrocarbon fuel) fuel gas containing methane (CH4) and a portion of the cathode gas (oxygen-containing gas) are supplied to the anode gas flow path 65. When the reforming feedstock fuel gas and the oxygen-containing gas are supplied to the anode gas flow path 65, a partial oxidation reaction occurs in the anode gas flow path 65, promoted by the partial oxidation catalyst 70. As will be described later, the partial oxidation reaction is an exothermic reaction, and therefore, by causing the partial oxidation reaction, the fuel cell stack 100 can be directly heated (warmed up) from the inside when the fuel cell stack 100 is started up.

[0028] FIG. 3 is an enlarged cross-sectional view of the circled portion in FIG. 1, illustrating the microstructure of the partial oxidation catalyst 70. As shown in FIG.

[0029] 3, the partial oxidation catalyst 70 is formed by supporting catalyst particles 72 on a support 71. The catalyst particles 72 can be supported by, for example, impregnation. As described above, the partial oxidation catalyst 70 is applied to the separator 60 in the anode gas flow path 65, i.e., the surface of the separator 60 facing the anode layer 40.

[0030] The catalyst particles 72 may be any known material, including, for example, one or more of nickel (Ni), iron (Fe), manganese (Mn), cobalt (Co), molybdenum (Mo), platinum (Pt), ruthenium (Ru), rhodium (Rh), iridium (Ir), and palladium (Pd).

[0031] The carrier 71 is made of an oxide, and any known oxide may be used, such as alumina (Al2O3), ceria (CeO2), zirconia (ZrO2), or a ceria-zirconia solid solution. The oxide carrier 71 suppresses carbon deposition from the fuel gas.

[0032] As described above, at the start-up of the fuel cell stack 100, the reforming raw material fuel gas and oxygen-containing gas are supplied to the anode gas flow channel 65, and a partial oxidation reaction occurs in the anode gas flow channel 65, promoted by the partial oxidation catalyst 70. The reaction formula of the partial oxidation reaction is shown in the following formula (1).

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[0033] As shown in formula (1), the partial oxidation reaction is an exothermic reaction that occurs when methane (CH4) contained in the reforming feedstock fuel gas reacts with oxygen (O2). The heat generated by the partial oxidation reaction is transferred to the fuel cell 10 via the separator 60 made of a thermally conductive material. This allows the fuel cell stack 100 to be directly heated from the inside to its operating temperature when it is started up. In other words, the heating time of the fuel cell stack 100 can be shortened compared to when air is heated with heat generated when fuel is combusted in the combustor and the heated air is supplied to the fuel cell stack 100. Therefore, the start-up time of the fuel cell stack 100 can be shortened.

[0034] However, when the reforming raw material and oxygen-containing gas are actually supplied to the anode gas flow channel 65 to cause a partial oxidation reaction, a phenomenon in which a localized high temperature occurs near the inlet of the anode gas flow channel 65 has been confirmed. This is thought to be because, although the partial oxidation reaction is expressed by the above-mentioned formula (1), when viewed microscopically, the following formulas (2), (3), and (4) occur. That is, the combustion reaction of formula (2), which generates a very large amount of heat, the steam reforming reaction of formula (3), and the dry reforming reaction of formula (4) occur. Because the amount of oxygen (O2) is large near the inlet of the anode gas flow channel 65, the combustion reaction of formula (2) becomes dominant. On the other hand, because oxygen (O2) is consumed by the combustion reaction upstream, the amount of oxygen (O2) decreases toward the downstream side of the anode gas flow channel 65, and the steam reforming reaction of formula (3) and the dry reforming reaction of formula (4) become dominant downstream. This is thought to be why a localized high temperature occurs near the inlet of the anode gas flow channel 65, where the combustion reaction is dominant.

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[0035] In this way, if the temperature near the inlet of the anode gas flow channel 65 becomes locally high due to the partial oxidation reaction, the temperature distribution in the fuel cell 10 may become uneven, which may result in a decrease in the output performance of the fuel cell 10. Furthermore, if the temperature in part of the anode gas flow channel 65 becomes too high, or if the temperature difference within the anode gas flow channel 65 becomes too large, there is a risk of physical defects occurring in the separators 60 that separate the multiple fuel cell cells 10.

[0036] Therefore, in this embodiment, a heat-resistant metal material 80 is disposed on the bottom surface of the inlet side of the anode gas flow channel 65 to prevent the inlet side of the anode gas flow channel 65 from becoming locally hot.

[0037] FIG. 4 is a partial cross-sectional view of the fuel cell stack 100 as seen from the side of the anode gas flow channel 65, and FIG. 5 is a partial cross-sectional view of the fuel cell stack 100 as seen from the side of the anode gas flow channel 65. B - B A cross-sectional view along the line in Fig. 6 is that of Fig. 4. A - A FIG.

[0038] 4, the anode gas during normal operation of the fuel cell stack 100 and the fuel gas and oxygen-containing gas used as reforming materials during startup flow from the inlet 651 to the outlet 652 of the anode gas flow channel 65. Although not shown in FIG. 4, the air (cathode gas) flowing through the cathode gas flow channel 64 flows in the same direction as the fuel gas and oxygen-containing gas, in parallel thereto. As described above, the anode gas flow channel 65 is prone to becoming hot near the inlet 651, so by flowing the air in the same direction as the fuel gas and oxygen-containing gas, the air can be efficiently heated via the separator 60.

[0039] As shown in Fig. 4, a plate-shaped heat-resistant metal material 80 is joined to the separator 60 on the bottom surface of the inlet side of the anode gas flow channel 65. The "inlet side" here refers to a range closer to the inlet 651 than half of the total length of the anode gas flow channel 65, and the position of the heat-resistant metal material 80 from the inlet 651 may be determined arbitrarily as long as it is within this range. The heat-resistant metal material 80 may be joined by any known method, and for example, the heat-resistant metal material 80 can be fixed to the separator 60 by welding. Hereinafter, the portion of the anode gas flow channel 65 where the heat-resistant metal material 80 is arranged will be referred to as the inlet side, and the portion where the heat-resistant metal material 80 is not arranged will be referred to as the outlet side.

[0040] The material forming the heat-resistant metal material 80 is not particularly limited as long as it has heat resistance, but preferably, austenitic stainless steel is used. Examples of austenitic stainless steel include SUS304, SUS316, Hastelloy, and Inconel. Austenitic stainless steel has higher oxidation resistance than ferritic stainless steel, but its thermal expansion coefficient differs greatly from that of the fuel cell 10. For this reason, if austenitic stainless steel is used as the material for the separator 60, there is a risk that the separator 60 will come off at the joints of the fuel cell 10 (such as the contact points with the metal support 50). Therefore, it is preferable to use austenitic stainless steel for the heat-resistant metal material 80 and ferritic stainless steel for the separator 60, as described above.

[0041] 4 and 5, the heat-resistant metal material 80 has a thickness that is approximately half the height of the portion of the anode gas flow channel 65 where the heat-resistant metal material 80 is not placed. A step 653 is formed at the boundary between the portion of the anode gas flow channel 65 where the heat-resistant metal material 80 is placed and the portion where the heat-resistant metal material 80 is not placed.

[0042] A partial oxidation catalyst 70 is applied to the upper surface of the heat-resistant metal material 80, i.e., the surface facing the anode layer 40. Furthermore, the separator 60 is not coated with the partial oxidation catalyst 70 on the inlet side of the anode gas flow channel 65 where the heat-resistant metal material 80 is disposed. On the other hand, as shown in FIG. 6 , the partial oxidation catalyst 70 is applied to the entire surface of the separator 60 facing the anode layer 40 on the outlet side of the anode gas flow channel 65 where the heat-resistant metal material 80 is not disposed.

[0043] When the fuel cell stack 100 is started up, if the reforming raw material fuel gas and oxygen-containing gas are supplied to the anode gas flow channel 65, the combustion reaction of the above formula (2), which generates a large amount of heat, becomes dominant near the inlet 651 of the anode gas flow channel 65, where the amount of oxygen is large. However, the heat generated by the combustion reaction is mitigated by the heat-resistant metal material 80, and the vicinity of the inlet 651 of the anode gas flow channel 65 is prevented from becoming locally hot.

[0044] Furthermore, at the inlet side of the anode gas flow channel 65, the partial oxidation catalyst 70 is applied only to the upper surface of the heat-resistant metal material 80, and at the outlet side of the anode gas flow channel 65, the partial oxidation catalyst 70 is applied to the entire surface of the separator 60. This makes it easier for the partial oxidation reaction to occur at the outlet side of the anode gas flow channel 65 than at the inlet side, further preventing the temperature near the inlet 651 of the anode gas flow channel 65 from becoming locally high.

[0045] Furthermore, the cross-sectional area of ​​the heat-resistant metal material 80 in the thickness direction is approximately half the cross-sectional area of ​​the anode gas flow channel 65 in the portion where the heat-resistant metal material 80 is not disposed. As a result, the cross-sectional area of ​​the anode gas flow channel 65 at the inlet side where the heat-resistant metal material 80 is disposed is approximately half that at the outlet side where the heat-resistant metal material 80 is not disposed. When fuel gas and oxygen-containing gas are supplied to the anode gas flow channel 65 during startup of the fuel cell stack 100, the gas flow rate increases at the inlet side, where the flow channel is narrower than at the outlet side. Because the provision of the heat-resistant metal material 80 increases the flow rate at the inlet side, the fuel gas and oxygen-containing gas are more diffused toward the outlet side at the stepped portion 653 where the flow channel is expanded, compared to when the heat-resistant metal material 80 is not disposed. This prevents the combustion reaction from concentrating only near the inlet 651 of the anode gas flow channel 65, and heat is dispersed in the gas flow direction.

[0046] The cross-sectional area of ​​the heat-resistant metal material 80 in the thickness direction is preferably approximately half the cross-sectional area of ​​the anode gas flow path 65 in the portion where the heat-resistant metal material 80 is not disposed, but is not necessarily limited to this. The thickness of the heat-resistant metal material 80 may be determined arbitrarily as long as a flow path cross-sectional area is formed that is large enough not to impede the flow of the anode gas, fuel gas, and oxygen-containing gas.

[0047] Fig. 7 is a graph showing the difference in temperature in the anode gas flow channel 65 depending on whether or not the heat-resistant metal material 80 is present. The horizontal axis of Fig. 7 is the distance L from the inlet 651 of the anode gas flow channel 65, and the distance from the inlet 651 to the outlet 652, i.e., the total length of the anode gas flow channel 65, is La. The vertical axis of Fig. 7 is the temperature T in the anode gas flow channel. Fig. 7 shows an example of the temperature distribution in the anode gas flow channel 65 when the heat-resistant metal material 80 is disposed up to the distance L and when the heat-resistant metal material 80 is not disposed, when a fuel gas and an oxygen-containing gas are supplied to the anode gas flow channel 65.

[0048] As shown in FIG. 7, when the heat-resistant metal material 80 is disposed near the inlet 651 of the anode gas flow channel 65, the temperature near the inlet 651 of the anode gas flow channel 65 is prevented from becoming locally too high.

[0049] Up to a distance L1, which is approximately one-quarter of the total length of the anode gas flow channel 65, the temperature difference between the temperature near the inlet 651 and the temperature at the distance L is smaller when the heat-resistant metal material 80 is disposed than when the heat-resistant metal material 80 is not disposed. On the other hand, when the distance at which the heat-resistant metal material 80 is disposed exceeds L1, the temperature difference between the temperature near the inlet 651 and the temperature at the distance L becomes almost the same as or even larger than when the heat-resistant metal material 80 is not disposed. Therefore, the heat-resistant metal material 80 is preferably disposed up to the distance L1, i.e., approximately one-quarter of the total length of the anode gas flow channel 65, but this is not necessarily limited to this. As described above, the distance at which the heat-resistant metal material 80 is disposed from the inlet 651 may be determined arbitrarily, as long as it is within the range from the inlet 651 to half the total length of the anode gas flow channel 65.

[0050] As described above, by disposing the heat-resistant metal material 80 on the inlet side of the anode gas flow channel 65, it is possible to prevent the temperature near the inlet 651 of the anode gas flow channel 65 from becoming locally high due to the partial oxidation reaction. In addition, the heat-resistant metal material 80 narrows the cross-sectional area of ​​the anode gas flow channel 65 on the inlet side, increasing the gas flow rate, thereby preventing the combustion reaction from concentrating only near the inlet 651.

[0051] Preferably, the amount of partial oxidation catalyst 70 per unit area applied to the heat-resistant metal material 80 is made smaller than the amount of partial oxidation catalyst 70 per unit area applied to the separator 60. This promotes the partial oxidation reaction more at the outlet side of the anode gas flow channel 65 where the partial oxidation catalyst 70 is applied to the separator 60 than at the inlet side where the heat-resistant metal material 80 is applied to the anode gas flow channel 65, and further suppresses uneven temperature distribution.

[0052] Preferably, the concentration of catalyst fine particles 72 supported on the carrier 71 is adjusted so that the concentration of the partial oxidation catalyst 70 applied to the heat-resistant metal material 80 is lower than the concentration of the partial oxidation catalyst 70 applied to the separator 60. This also promotes the partial oxidation reaction more at the outlet side of the anode gas flow channel 65 where the partial oxidation catalyst 70 is applied to the separator 60 than at the inlet side where the partial oxidation catalyst 70 is applied to the heat-resistant metal material 80, and further suppresses uneven temperature distribution.

[0053] Preferably, the partial oxidation catalyst 70 applied to the heat-resistant metal material 80 is prepared so that palladium (Pd) accounts for the largest percentage of each substance per unit weight of the catalyst fine particles 72 among the materials constituting the catalyst fine particles 72. For example, if the catalyst fine particles 72 are made of palladium (Pd) and platinum (Pt), the percentage of Pd per unit weight of the catalyst fine particles 72 is prepared to be larger than the percentage of Pt. On the other hand, the partial oxidation catalyst 70 applied to the separator 60 is prepared so that the percentage of Pd per unit weight of the catalyst fine particles 72 is smaller than that of the other materials. Pd has high activity in the combustion reaction represented by the aforementioned formula (2), but low activity in the steam reforming reaction and dry reforming reaction represented by formulas (3) and (4). In contrast, the materials constituting the catalyst fine particles 72 other than Pd have high activity in the steam reforming reaction and dry reforming reaction. During startup of the fuel cell stack 100, the combustion reaction (Equation (1)) occurs mainly on the heat-resistant metal material 80, so there is no need to load a large amount of Pd onto the partial oxidation catalyst 70 applied to the downstream separator 60. Therefore, by increasing the percentage of Pd in ​​the catalyst fine particles 72 on the upstream side where the heat-resistant metal material 80 is located and decreasing the percentage of Pd on the downstream side, the partial oxidation reaction can be carried out efficiently. Furthermore, the material for the catalyst fine particles 72 can be saved.

[0054] Furthermore, when fuel gas and oxygen-containing gas are supplied to the anode gas flow channel 65 during startup of the fuel cell stack 100, the ratio (O2 / C) of the amount of oxygen (O2) molecules to the amount of carbon atoms (C) in the hydrocarbon fuel is preferably adjusted to 1.0 or less by a control unit (not shown) of the fuel cell system. If O2 / C exceeds 0.5, the amount of hydrogen produced by the partial oxidation reaction increases, raising the adiabatic flame temperature. If O2 / C exceeds 1.0, the heat resistance of stainless steel is exceeded. Therefore, by adjusting O2 / C to 1.0 or less, excessive heating of the separator 60 can be more reliably prevented.

[0055] According to the solid oxide fuel cell stack 100 of the first embodiment described above, the following effects can be obtained.

[0056] In the fuel cell stack (solid oxide fuel cell) 100, a heat-resistant metal material 80 is disposed on the bottom surface of the inlet side of the anode gas flow path (fuel flow path) 65, and a partial oxidation catalyst 70 is applied to the surface of the separator 60 and the heat-resistant metal material 80 that form the anode gas flow path (fuel flow path) 65, facing the anode electrode layer 40. Therefore, even if a partial oxidation reaction occurs inside the fuel cell stack (solid oxide fuel cell) 100 (fuel flow path 65), the heat-resistant metal material 80 prevents the inlet side of the anode gas flow path (fuel flow path) 65 from becoming locally hot. Therefore, the temperature of the fuel cell stack (solid oxide fuel cell) 100 can be raised in a short time, while preventing the temperature distribution of the fuel cell 10 from becoming uneven.

[0057] Furthermore, since the heat-resistant metal material 80 is disposed, the flow path cross-sectional area on the inlet side of the anode gas flow path (fuel flow path) 65 is reduced, and the gas flow velocity on the inlet side is higher than on the outlet side. As a result, when the fuel cell stack (solid oxide fuel cell) 100 is started up, the fuel gas and oxygen-containing gas are diffused further toward the outlet side, and the combustion reaction is prevented from concentrating only near the inlet 651. Therefore, it is possible to further prevent the temperature distribution of the fuel cell 10 from becoming uneven when the fuel cell stack (solid oxide fuel cell) 100 is started up.

[0058] In the fuel cell stack (solid oxide fuel cell) 100, the separator 60 that forms the anode gas flow path (fuel flow path) 65 between two adjacent fuel cell cells 10 is an uneven member. Because the separator 60 has an uneven (including curved) structure, even if the metal support 50 or the like is displaced, the separator 60 can follow the displacement.

[0059] In the fuel cell stack (solid oxide fuel cell) 100, the partial oxidation catalyst 70 is applied only to the heat-resistant metal material 80 on the inlet side of the anode gas flow path (fuel flow path) 65. This prevents the partial oxidation reaction (combustion reaction) from concentrating on the inlet side compared to when the partial oxidation catalyst 70 is applied to both the separator 60 and the heat-resistant metal material 80 on the inlet side of the anode gas flow path (fuel flow path) 65. This further prevents the temperature from becoming locally high near the inlet 651 of the anode gas flow path (fuel flow path) 65.

[0060] In the fuel cell stack (solid oxide fuel cell) 100, the partial oxidation catalyst 70 is applied to the entire surface of the separator 60 facing the anode layer 40 on the outlet side of the anode gas flow channel (fuel flow channel) 65. This promotes the partial oxidation reaction more on the outlet side of the anode gas flow channel (fuel flow channel) 65 than when the partial oxidation catalyst 70 is applied only to the surface of the separator 60 parallel to the anode layer 40. Therefore, the partial oxidation reaction occurs more easily on the outlet side of the anode gas flow channel (fuel flow channel) 65 than on the inlet side, further suppressing the local high temperature near the inlet 651 of the anode gas flow channel (fuel flow channel) 65.

[0061] In this embodiment, the heat-resistant metal material 80 is plate-shaped, but is not limited to this. For example, when the anode gas flow path 65 has a curved cross section in the flow path direction as shown in Fig. 8, it is preferable to use a linear heat-resistant metal material 80 that matches the flow path shape.

[0062] Furthermore, in this embodiment, the separator 60 has an uneven (including curved) structure, but is not limited to this. For example, as shown in Fig. 9, the connecting portion 63 may be provided with two bent portions 631, 632 to make the connecting portion 63 bendable, thereby giving the separator 60 a springy structure. This allows the separator 60 to better absorb expansion displacement in the stacking direction of the fuel cell 10.

[0063] Furthermore, in this embodiment, the separator 60 is configured to form the anode gas flow path 65 and the cathode gas flow path 64, but the separator 60 may be configured to form only the anode gas flow path 65. In this case, a plurality of anode gas flow paths 65 surrounded by the separator 60 and the metal support 50 are formed between each fuel cell 10, and the cathode gas is supplied to the cathode layer 30 from one end of the fuel cell stack 100 in the horizontal direction.

[0064] Furthermore, as in this embodiment, it is preferable that the fuel gas and oxygen-containing gas flowing through the anode gas flow channel 65 and the air (cathode gas) flowing through the cathode gas flow channel 64 flow in the same direction and parallel to each other, but this is not necessarily limited to this. That is, the fuel gas and oxygen-containing gas may be configured to flow in opposite directions (reverse directions) to the cathode gas.

[0065] Furthermore, as in this embodiment, it is preferable that the partial oxidation catalyst 70 be applied only to the heat-resistant metal material 80 on the inlet side of the anode gas flow channel 65, and that the partial oxidation catalyst 70 be applied to the entire surface of the separator 60 facing the anode layer 40 on the outlet side, but this is not necessarily limited to this. For example, the partial oxidation catalyst 70 may be applied to both the heat-resistant metal material 80 and the separator 60 on the inlet side of the anode gas flow channel 65. Furthermore, for example, the partial oxidation catalyst 70 may be applied only to the surface of the separator 60 that is parallel to the anode layer 40 on the outlet side of the anode gas flow channel 65.

[0066] Furthermore, in this embodiment, the separator 60 and the heat-resistant metal material 80 are coated with the partial oxidation catalyst 70, but in addition to the partial oxidation catalyst 70, the separator 60 and the heat-resistant metal material 80 may be coated with a separate steam reforming catalyst. In this case, steam reforming of fuel is performed inside the fuel cell stack 100, eliminating the need to provide a separate reformer, and allowing the fuel cell stack 100 to be made smaller.

[0067] (Second embodiment) A solid oxide fuel cell stack 100 according to a second embodiment will be described with reference to Figures 10 and 11. This embodiment differs from the first embodiment in that a heat resistance layer 90 is provided between a heat-resistant metal material 80 and a separator 60. Elements similar to those in the first embodiment are designated by the same reference numerals, and their description will be omitted.

[0068] FIG. 10 is a schematic diagram of a solid oxide fuel cell stack according to the second embodiment, and FIG. 11 is a cross-sectional view taken along line CC in FIG.

[0069] As shown in Figures 10 and 11, a plate-shaped heat resistance layer 90 is formed below the bottom surface of the heat-resistant metal material 80 arranged on the inlet side of the anode gas flow path 65, i.e., between the heat-resistant metal material 80 and the separator 60.

[0070] The material for forming the heat resistance layer 90 is not particularly limited as long as it has low thermal conductivity, but preferably has a thermal conductivity lower than that of metal and a thermal expansion coefficient between that of the separator 60 and the heat-resistant metal material 80. For example, if the separator 60 is ferritic stainless steel and the heat-resistant metal material 80 is austenitic stainless steel, a ceramic glass or the like is used, which has a thermal conductivity lower than that of metal and a thermal expansion coefficient intermediate between that of ferritic stainless steel and austenitic stainless steel.

[0071] The bonding method for the thermal resistance layer 90 is not particularly limited, but for example, in the case of ceramic glass, it is first heated to soften it, and then further heated to a high temperature to sinter and bond it.

[0072] The heat-resistant metal material 80 disposed on the inlet side of the anode gas flow channel 65 is actually a thin plate (e.g., a thickness of 5 mm or less). Therefore, even if the heat-resistant metal material 80 is disposed between the partial oxidation catalyst 70 and the separator 60, heat may still be transferred to the separator 60 due to a thermal gradient. However, in this embodiment, the heat-resistant layer 90, which has low thermal conductivity, is formed between the heat-resistant metal material 80 and the separator 60, thereby more effectively preventing the heat of the partial oxidation reaction (combustion reaction) from being transferred to the separator 60 in a concentrated manner near the inlet of the anode gas flow channel 65. Furthermore, for example, by using ceramic glass, whose thermal expansion coefficient is between that of the separator 60 and the heat-resistant metal material 80, for the heat-resistant layer 90, peeling of the heat-resistant layer 90 due to thermal expansion of the separator 60 or the heat-resistant metal material 80 can be prevented.

[0073] According to the solid oxide fuel cell stack 100 of the second embodiment described above, the following effects can be obtained.

[0074] In the fuel cell stack (solid oxide fuel cell) 100, a heat resistance layer 90 is provided between the heat-resistant metal material 80 arranged on the inlet side of the anode gas flow channel 65 and the separator 60. This makes it possible to further suppress the heat of the partial oxidation reaction (combustion reaction) from being transferred to the separator 60 in a concentrated manner near the inlet of the anode gas flow channel 65.

[0075] In this embodiment, the thermal resistance layer 90 is a plate-like layer, but the shape of the thermal resistance layer 90 is not limited to this. For example, as shown in FIG. 12 , the thermal resistance layer 90′ may be formed by welding the heat-resistant metal material 80 and the separator 60 together with a heat-resistant layer-forming member 91 in a dot pattern. In this case, the heat-resistant layer-forming member 91 is welded to the separator 60 and the heat-resistant metal material 80 from the rear (below the bottom surface) of the separator 60 using a laser. This forms the thermal resistance layer 90′ as a space between the separator 60 and the heat-resistant metal material 80. By forming such a space (thermal resistance layer 90′) between the separator 60 and the heat-resistant metal material 80, the heat transfer area from the heat-resistant metal material 80 to the separator 60 is reduced, and heat generated in the partial oxidation catalyst 70 is less likely to be transferred to the separator 60. That is, the heat of the partial oxidation reaction (combustion reaction) near the inlet of the anode gas flow channel 65 can be further prevented from being transmitted to the separator 60 in a concentrated manner.

[0076] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate 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 embodiments.

[0077] Furthermore, although the above-described embodiments have been described as separate embodiments, they may be combined as appropriate. [Explanation of symbols]

[0078] 10 Fuel cell 20 Solid electrolyte layer 30 Cathode layer 40 Anode layer 50 Metal support 60 Separator 65 Anode gas flow path (fuel flow path) 70 Partial oxidation catalyst 80 Heat-resistant metal materials 90 Heat resistance layer 100 Fuel Cell Stack (Fuel Cell)

Claims

1. A solid oxide fuel cell including a plurality of fuel cell units each formed by stacking an anode layer, a cathode layer, and a solid electrolyte layer sandwiched between the anode layer and the cathode layer on a metal support disposed on the anode layer side, the fuel cell units being stacked with a separator interposed therebetween, the separator forms a fuel flow path between two adjacent fuel cells for supplying fuel to the anode layer, a heat-resistant metal material is disposed only on a surface of the fuel flow channel that faces the anode layer via the metal support, at an inlet side of the fuel flow channel; a partial oxidation catalyst is applied to the separator and the heat-resistant metal material on a surface facing the anode layer via the metal support; Solid oxide fuel cell.

2. 2. The solid oxide fuel cell according to claim 1, the separator is an uneven member including a plurality of first contact portions that contact the anode layer side of one of the two adjacent fuel cell units, a plurality of second contact portions that contact the cathode layer side of the other fuel cell unit, and a connecting portion that connects the first contact portions and the second contact portions; the fuel flow path is defined by a space surrounded by the second contact portion and the connecting portion. Solid oxide fuel cell.

3. 3. The solid oxide fuel cell according to claim 1, a cross-sectional area of ​​the heat-resistant metal material in a stacking direction of the fuel cell is half a cross-sectional area of ​​the fuel flow path; Solid oxide fuel cell.

4. 4. A solid oxide fuel cell according to claim 1, The heat-resistant metal material is in the form of a plate or wire. Solid oxide fuel cell.

5. 5. A solid oxide fuel cell according to claim 1, the partial oxidation catalyst is applied only on the heat-resistant metal material at the inlet side of the fuel flow passage; Solid oxide fuel cell.

6. 6. A solid oxide fuel cell according to claim 1, The partial oxidation catalyst is applied to the entire surface of the separator facing the anode layer at the outlet side of the fuel flow channel. Solid oxide fuel cell.

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