JP7501091B2 - Fuel cell structure and method for manufacturing the fuel cell structure - Google Patents

Description

The present invention relates to a fuel cell structure and a method for manufacturing a fuel cell structure.

Patent Document 1 proposes a unit cell in which a fuel electrode and an oxidizer electrode are arranged to face each other with an electrolyte matrix interposed between them. In this unit cell, a fuel reforming catalyst is filled in a fuel passage provided in the fuel electrode. In particular, in the unit cell of Patent Document 1, a fuel reforming catalyst with a lower carbon deposition tendency is arranged on the upstream side of the fuel passage in the fuel flow direction than on the downstream side.

Japanese Patent Application Laid-Open No. 63-310574

However, fuel reforming catalysts with low carbon deposition are made of catalytic materials (such as barium) that are reactive to carbon oxides (especially carbon dioxide). This poses the problem that the catalytic materials deteriorate as a result of reacting with carbon oxides.

In view of these circumstances, the object of the present invention is to realize a fuel cell structure that can suppress both carbon deposition and catalyst deterioration.

According to one aspect of the present invention, there is provided a fuel cell structure including an internal reforming type fuel cell having an electrode layer and an electrolyte layer supported on one side of a metal support layer and a separator attached to the other side, and a fuel flow path formed in a space between the other side of the metal support layer and a surface of the separator. This fuel cell structure includes a first reforming catalyst layer provided on the other side of the metal support layer in an upstream region of the fuel flow path, extending over a predetermined range in the gas flow direction of the fuel flow path and in the electrode width direction perpendicular to the gas flow direction, a second reforming catalyst layer provided on the other side of the metal support layer in a downstream region of the fuel flow path, and a fuel outflow prevention film provided on an end of the first reforming catalyst layer in the electrode width direction and preventing fuel from bypassing the first reforming catalyst layer and outflowing to the metal support layer. The first reforming catalyst layer is made of a material that is more effective at preventing carbon deposition due to a reforming reaction than the second reforming catalyst layer, and the fuel outflow prevention film includes a carbon oxide absorbent that absorbs carbon oxides generated by the reforming reaction in the first reforming catalyst layer.

The present invention makes it possible to realize a fuel cell structure that can suppress both carbon deposition and catalyst deterioration.

FIG. 1 is a diagram illustrating the configuration of a fuel cell structure common to each embodiment and modification. FIG. 2 is an enlarged view of a main portion of the fuel cell structure (the portion circled in FIG. 1). FIG. 3 is a diagram illustrating a detailed configuration of the fuel cell structure according to the first embodiment. FIG. 4 is a diagram showing a schematic structure of the first reforming catalyst layer and the fuel outflow prevention film. FIG. 5 is a diagram for explaining the function and effect obtained when the end portion of the first reforming catalyst layer overlaps with the fuel outflow prevention film. FIG. 6 is a diagram illustrating each step in the manufacturing method of the fuel cell structure. FIG. 7A is a diagram illustrating the configuration of a fuel cell structure according to a second embodiment. FIG. 7B is a partially enlarged view of FIG. 7A(b). FIG. 8 is a diagram illustrating the configuration of a fuel cell structure according to the first modification. FIG. 9 is a diagram for explaining the technical significance of the manufacturing method according to the second modification. FIG. 10 is a diagram illustrating the configuration of a fuel cell stack according to the third modification.

Each embodiment of the present invention will be described in detail below with reference to the drawings.

First Embodiment
1 is a diagram illustrating the configuration of a fuel cell stack 10 as a fuel cell structure according to this embodiment. For ease of explanation, an XYZ orthogonal coordinate system is shown in each figure below. In addition, the X-axis direction in the figure will be referred to as the "electrode width direction X", the Y-axis direction as the "gas flow direction Y", and the Z-axis direction as the "stacking direction Z" as necessary.

As shown in the figure, the fuel cell stack 10 of this embodiment is a direct internal reforming stacked fuel cell in which multiple (four are shown in FIG. 1) cell units 20 and separators 30 configured as solid oxide fuel cells (SOFC) are stacked in sequence.

In particular, the fuel cell stack 10 of this embodiment can be used as a stationary power source for various electrical devices, and as a power source for mobile vehicles such as electric cars and hybrid cars.

<Cell unit 20>
The cell unit 20 of this embodiment is configured by stacking a fuel electrode layer (anode electrode layer 24), an electrolyte layer 26, and an air electrode layer (cathode electrode layer 28) in this order on one surface (first surface 22a) of the metal support layer 22. In particular, the fuel cell stack 10 of this embodiment is configured as a metal-supported fuel cell in which a separator 30 is provided on the other surface (second surface 22b) of the metal support layer 22 of the cell unit 20, and adjacent cell units 20 are stacked with the separator 30 interposed therebetween. A fuel gas flow path 32 for supplying fuel gas is configured as a space between the second surface 22b of the metal support layer 22 and the first surface 30a of the separator 30. An oxidant gas flow path 34 for supplying oxidant gas (air) is configured as a space between the second surface 30b of the separator 30 and the cathode electrode layer 28 of the adjacent cell unit 20.

<Metal Support Layer 22>
The metal support layer 22 supports the anode electrode layer 24, the electrolyte layer 26, and the cathode electrode layer 28, and has a first reforming catalyst layer 40 and a second reforming catalyst layer 42 (shown in FIG. 2 and thereafter) provided on a second surface 22b in contact with the fuel gas flow field 32. The first reforming catalyst layer 40 and the second reforming catalyst layer 42 will be described in detail later.

The metal support layer 22 is formed from a porous metal material that has a certain mechanical strength for supporting the anode electrode layer 24, the electrolyte layer 26, and the cathode electrode layer 28, and has gas permeability and electronic conductivity. For example, the metal support layer 22 may be made of metal particles or metal fibers solidified by sintering or pressing, or a metal plate made porous by drilling holes through an etching process or mechanical process. In particular, it is preferable that the metal support layer 22 be made from a porous body made by sintering metal particles.

Specific examples of the metal material constituting the metal support layer 22 include iron (Fe), chromium (Cr), nickel (Ni), titanium (Ti), and alloys thereof (especially stainless steel). More specifically, examples of the metal material constituting the metal support layer 22 include ferritic stainless steel. In particular, examples of the ferritic stainless steel include SUS400 series such as SUS410, SUS420, SUS430, and SUS440. More preferably, Fe-Cr alloys such as Crofer (registered trademark) 22 alloy (manufactured by ThyssenKrupp-VDM), ZMG (registered trademark) 232G10 (manufactured by Hitachi Metals, Ltd.), ITM (manufactured by Plansee), or SanergyHT (manufactured by Sandvik) are used.

<Anode Electrode Layer 24>
The anode electrode layer 24 is a fuel electrode, and functions to react oxide ions derived from the fuel gas and the oxidant gas to generate oxides of the fuel gas and to extract electrons. The anode electrode layer 24 is configured as a plate-shaped porous member provided so as to contact the lower surface of the electrolyte layer 26 in the figure. The anode electrode layer 24 is also configured to have resistance to a reducing atmosphere, and to have high gas permeability for passing the fuel gas, electronic conductivity, and ion conductivity. Furthermore, the anode electrode layer 24 has a catalytic function for an oxidation reaction that causes the fuel gas to react with oxide ions.

Examples of the material of the anode electrode layer 24 include metals such as nickel or iron, or cermets of the metals and solid oxide ceramics. Examples of the solid oxide ceramics include stabilized zirconia doped with rare earth oxides (e.g., one or _more materials selected from the group consisting of _Y2O3 , _{Sc2O3 , Gd2O3} , _Sm2O3 , _Yb2O3 , and _Nd2O3 ), ceria-based solid solutions, _{and perovskite} -type oxides _{( e.g.} , _SrCeO3 , _BaCeO3 , _CaZrO3 , or _SrZrO3 ).

The fuel that can be used in the fuel cell stack 10 of this embodiment is any hydrocarbon fuel that is a source of hydrogen generation, particularly alkanes, alkenes, alkynes, or aromatic hydrocarbons, as well as alcohols, aldehydes, ketones, ethers, or the like that contain functional groups that contain elements other than hydrocarbons (e.g., oxygen). In particular, methane ( _CH4 ) fuel is used in this embodiment.

<Electrolyte layer 26>
The electrolyte layer 26 has a function of separating the fuel gas from the oxidant gas. The electrolyte layer 26 is configured to allow oxide ions to pass from the cathode electrode layer 28 to the anode electrode layer 24, but not allow gas and electrons to pass through.

The electrolyte layer 26 is densely constructed to block anode gas and cathode gas and exhibit high ionic conductivity. More specifically, the density of the electrolyte layer 26 is not particularly limited as long as it has gas blocking properties, but is preferably 90% or more, more preferably 96% or more, and particularly preferably 98% or more. The electrolyte layer 26 is formed as a plate having a thickness of about several tens of microns.

Examples of materials constituting the electrolyte layer 26 include solid oxide ceramics _such as stabilized zirconia _doped with rare earth oxides (e.g., one or more materials selected from the group consisting of _{Y2O3 , Sc2O3} , _Gd2O3 , _{Sm2O3 , Yb2O3} , and _Nd2O3 ), ceria _- based solid solutions, or perovskite-type oxides ( _e.g. , _SrCeO3 , _BaCeO3 , _CaZrO3 , _SrZrO3 , etc.). More specifically, examples of materials that _can be used for the electrolyte layer 26 include YSZ (yttria-stabilized zirconia: _{Zr1- xYxO2} ), SSZ (scandium-stabilized zirconia: Zr1 _{- xScxO2} ), SDC (samarium-doped ceria: Ce1 _{- xSmxO2} ), GDC (gadolinium-doped ceria: _{Ce1- xGdxO2 )} , and LSGM (lanthanum strontium _magnesium gallate: _{La1 - xSrxGa1 - yMgyO3} ) _.

<Cathode electrode layer 28>
The cathode electrode layer 28 is an oxidizer electrode, and serves to convert oxygen molecules into oxide ions by reacting an oxidizer gas (particularly air) with electrons. The cathode electrode layer 28 is configured as a plate-shaped porous member provided in contact with the upper surface of the electrolyte layer 26 in the stacking direction Z. The cathode electrode layer 28 is also configured to be resistant to an oxidizing atmosphere, and to have high gas permeability for passing an oxidizer gas, electronic conductivity, and ion conductivity. Furthermore, the cathode electrode layer 28 has a catalytic function for a reduction reaction that converts oxygen molecules into oxygen ions.

The material of the cathode electrode layer 28 may be, for example, an oxide of one metal selected from the group consisting of lanthanum, strontium, manganese (Mn), and cobalt, or an alloy of two or more metals. In particular, lanthanum strontium cobalt iron composite oxide (LSCF) may be used as the material of the cathode electrode layer 28.

<Separator 30>
The separator 30 is configured as a member having an uneven cross section extending in the electrode width direction X. With such an uneven structure, a fuel gas flow path 32 is formed between the first surface 30a of the separator 30 and the second surface 22b of the metal support layer 22, and an oxidant gas flow path 34 is formed between the second surface 30b of the separator 30 and the first surface 22a of the metal support layer 22. The separator 30 is formed by press molding a conductive metal material such as iron or chromium. In particular, the first surface 30a of the separator 30 in this embodiment has protrusions 30c that come into contact with the first surface 22a of the metal support layer 22.

<First reforming catalyst layer 40 and second reforming catalyst layer 42>
2 is an enlarged view of a main portion (circled portion in FIG. 1) of the fuel cell stack 10. As shown in the figure, on the second surface 22b of the metal support layer 22 of the fuel cell stack 10, a second reforming catalyst layer 42 is provided in an upstream region _Au relatively close to the fuel gas inlet 32a in the fuel gas flow passage 32, and in a downstream region _Ad of the fuel gas flow passage 32 relatively far from the fuel gas inlet 32a in the first reforming catalyst layer 40.

The first reforming catalyst layer 40 is made of a material that promotes the reforming reaction that converts fuel gas into hydrogen gas while suppressing carbon deposition. In particular, the first reforming catalyst layer 40 is made by supporting fine catalyst particles (catalyst particles 40b) on a support (catalyst support 40a) made of an oxide.

The catalyst carrier 40a of the first reforming catalyst layer 40 is composed of, for example, a metal oxide such as barium oxide (BaO), magnesium oxide (MgO), or calcium oxide (CaO), _a mixture of one or more of the metal _oxides , or a solid solution of these. In particular, the catalyst carrier 40a of the first reforming catalyst layer 40 is preferably composed of BZCY ( _{BaZrxCeyYzOw :} x, y, z, and w are any stoichiometric composition).

The catalyst particles 40b of the first reforming catalyst layer 40 are composed of fine particles (particularly nanoparticles) composed of transition metals such as iron (Fe), nickel (Ni), cobalt (Co), copper (Cu), molybdenum (Mo), or lanthanum (La), precious metals such as ruthenium (Ru), platinum (Pt), rhodium (Rh), iridium (Ir), silver (Ag), or palladium (Pd), or a mixture of one or more of these metals.

On the other hand, the second reforming catalyst layer 42 is made of a material that promotes a reforming reaction (particularly a steam reforming reaction) that converts fuel gas into hydrogen gas. In particular, the support of the second reforming catalyst layer 42 is made of alumina or the like. The catalyst particles of the second reforming catalyst layer 42 are made of fine particles (particularly nanoparticles) made of, for example, transition metals such as iron (Fe), nickel (Ni), cobalt (Co), or copper (Cu), rare earth elements such as lanthanum (La), precious metals such as ruthenium (Ru), platinum (Pt), rhodium (Rh), iridium (Ir), silver (Ag), or palladium (Pd), or a mixture of one or more of these.

Here, the significance of providing the first reforming catalyst layer 40 in the upstream region _Au of the fuel gas flow channel 32 and the second reforming catalyst layer 42 for promoting the steam reforming reaction in the downstream region _Ad will be described.

In a direct internal reforming type SOFC such as the fuel cell stack 10 of this embodiment, a hydrocarbon fuel (particularly methane fuel) is reformed (mainly a steam reforming reaction) while the fuel flows through the fuel gas flow passage 32 inside the stack. This reforming reaction is an endothermic reaction that produces hydrogen and carbon oxide components (CO, _CO2 , etc.) by reacting a methane component with water, as shown in the following chemical formula (1).

[Chemical formula 1]
CH ₄ + H ₂ O → CO + 3H ₂ -Q ... (1)

Therefore, if sufficient moisture is not secured from the viewpoint of reacting the methane component, the steam reforming reaction does not proceed, and an unintended reaction with the catalyst material occurs, and carbon deposition, which is a factor of the deterioration of power generation performance, may occur on the catalyst surface. In particular, in the case of a direct internal reforming type SOFC, in the upstream region _Au of the fuel gas flow passage 32, which is relatively close to the fuel gas inlet 32a, the reforming of the fuel gas does not proceed sufficiently, and the power generation reaction is difficult to occur. Therefore, compared to the downstream region _Ad away from the fuel gas inlet 32a, there is a tendency that less water is generated by power generation and moisture is insufficient. As a result, in the upstream region _Au , carbon deposition due to an unintended reaction between the methane component and the catalyst material is more likely to occur than in the downstream region _Ad .

Therefore, in the fuel cell stack 10 of this embodiment, the first reforming catalyst layer 40, which is more active and has a greater carbon deposition suppression effect than a normal reforming catalyst material, is disposed in the upstream region _Au of the fuel gas flow channel 32 where moisture is easily insufficient. This makes it possible to generate hydrogen required for power generation while suppressing carbon deposition even in the upstream region _Au where moisture is scarce.

On the other hand, the inventors have found a problem that the metal material contained in the first reforming catalyst layer 40, which has a high carbon deposition suppression effect, reacts with carbon oxides such as carbon monoxide or carbon dioxide generated in the reforming reaction to generate metal carbonates such as _BaCO3 , _CaCo3 , or _MgCO3 , which deteriorate the catalyst. As a result of intensive study, the inventors have developed the fuel cell stack 10 of this embodiment, which has a configuration that can solve this problem. The configuration of the fuel cell stack 10 that solves this problem will be described in detail below.

In this specification, the "upstream region _Au of the fuel gas flow path 32" refers to a region close to the fuel gas inlet 32a to the extent that a certain amount of produced water cannot be secured, which is determined from the standpoint of ensuring appropriate progress of the steam reforming reaction of the methane component. In other words, the "upstream region _Au of the fuel gas flow path 32" corresponds to a region where carbon deposition occurs beyond an allowable limit from the standpoint of ensuring the power generation performance required of the fuel cell stack 10, assuming that a second reforming catalyst layer 42 that promotes the steam reforming reaction is disposed.

On the other hand, the "downstream region A _d of the fuel gas flow passage 32" refers to a region far enough from the fuel gas inlet 32a that a certain amount of generated water can be secured, which is determined from the viewpoint of appropriately progressing the steam reforming reaction of the methane component. In other words, the "downstream region A _d of the fuel gas flow passage 32" corresponds to a region where carbon deposition is below an allowable limit from the viewpoint of securing the power generation performance required of the fuel cell stack 10, even if the second reforming catalyst layer 42 that promotes the steam reforming reaction is disposed. The specific position that is the boundary between the "upstream region A _u of the fuel gas flow passage 32" and the "downstream region A _d of the fuel gas flow passage 32" is appropriately determined depending on the design of the fuel cell stack 10, and can be set, for example, to an approximately central position in the gas flow direction Y of the cell unit 20 (approximately the middle position between the fuel gas inlet 32a and the fuel gas outlet 32b).

Fig. 3 is a diagram for explaining a detailed configuration of the fuel cell stack 10 of this embodiment. In particular, Fig. 3 shows a schematic configuration of the fuel cell stack 10 shown in Fig. 2 when viewed along the gas flow direction Y. As shown in the figure, in the fuel cell stack 10 of this embodiment, a first reforming catalyst layer 40 is provided on the second surface 22b of the metal support layer 22 in the upstream region _Au of the fuel gas flow field 32 so as to extend over a predetermined range in the electrode width direction X and the gas flow direction Y. In particular, a plurality of first reforming catalyst layers 40 (three in Fig. 3) are provided to avoid the portion where the protruding portion 30c of the separator 30 is joined to the second surface 22b of the metal support layer 22 in the electrode width direction X.

Furthermore, a fuel leakage prevention film 44 is provided at the end 41 (particularly both ends 41, 41) of the first reforming catalyst layer 40 in the electrode width direction X. The fuel leakage prevention film 44 is made of a carbon oxide absorbent that has a certain degree of thermal fluidity and absorbs carbon oxides. Specifically, examples of the carbon oxide absorbent that constitutes the fuel leakage prevention film 44 include alkali metals or alkaline earth metals such as barium (Ba), calcium (Ca), or magnesium (Mg).

In particular, the fuel outflow prevention film 44 is provided so as to fill the space between the end 41 of the first reforming catalyst layer 40 and the joint portion (near the welded portion 46) between the second surface 22b of the metal support layer 22 and the separator 30.

Figure 4 is a diagram showing the structure of the first reforming catalyst layer 40 and the fuel leakage prevention film 44. As shown in the figure, the first reforming catalyst layer 40 has a structure in which catalyst particles 40b are supported on the outer surface of a catalyst carrier 40a. In addition, an end 41 of the first reforming catalyst layer 40 protrudes in the stacking direction Z so as to overlap a part of the fuel leakage prevention film 44.

With this structure, carbon oxides generated by the reforming reaction in the first reforming catalyst layer 40 are absorbed by the fuel outflow prevention film 44. Therefore, it is possible to suppress catalyst deterioration caused by unintended reactions between carbon oxides and the catalyst material.

In addition, according to the fuel cell stack 10 of this embodiment, the fuel leakage prevention film 44 is provided at the end 41 of the first reforming catalyst layer 40, so that the fuel gas (hydrocarbon gas) flowing through the fuel gas flow passage 32 is prevented from bypassing the end 41 (particularly both ends 41, 41) of the first reforming catalyst layer 40 and flowing toward the metal support layer 22. This makes it possible to prevent carbon deposition caused by the contact of the fuel gas with the metal support layer 22. In particular, in the fuel cell stack 10 of this embodiment, the fuel leakage prevention film 44 is sandwiched between the end 41 of the first reforming catalyst layer 40 and the second surface 22b of the metal support layer 22, so that the sealing function against the leakage of fuel gas by the fuel leakage prevention film 44 is further improved, and carbon deposition in the metal support layer 22 is more reliably suppressed.

Furthermore, by configuring the end 41 of the first reforming catalyst layer 40 described above to overlap with the fuel outflow prevention film 44 in the stacking direction Z, further effects described below are achieved.

5 is a diagram for explaining the effect of the end 41 of the first reforming catalyst layer 40 overlapping the fuel leakage prevention film 44. In particular, FIG. 5(a) shows an example in which the end 41 of the first reforming catalyst layer 40 does not overlap the fuel leakage prevention film 44, and in particular an example in which the fuel leakage prevention film 44 is configured to be thicker than the end 41 of the first reforming catalyst layer 40 (an example in which the thickness D2 of the end 41 is equal to or smaller than the thickness D1 of the fuel leakage prevention film 44). On the other hand, FIG. 5(b) shows a configuration in which the end 41 of the first reforming catalyst layer 40 overlaps the fuel leakage prevention film 44 (the configuration of the fuel cell stack 10 of this embodiment). More specifically, in the example shown in FIG. 5(b), the end 41 of the first reforming catalyst layer 40 is configured to be thicker than the fuel leakage prevention film 44. That is, the thickness D2 of the end 41 of the first reforming catalyst layer 40 is configured to be larger than the thickness D1 of the fuel leakage prevention film 44.

Here, the fuel leakage prevention film 44 has a certain fluidity in a high temperature environment in order to provide a filling property from the viewpoint of realizing the function of sealing between the end 41 of the first reforming catalyst layer 40 and the surface of the metal support layer 22. Therefore, in the configuration of FIG. 5(a), it is assumed that the fuel leakage prevention film 44 flows toward the first reforming catalyst layer 40 (in the direction shown by the thick arrow) and blocks the pores of the first reforming catalyst layer 40, thereby reducing the catalyst performance. In contrast, in the configuration of FIG. 5(b), the end 41 of the first reforming catalyst layer 40 acts to block the inflow of the fuel leakage prevention film 44, and the occurrence of the phenomenon of blocking the pores of the first reforming catalyst layer 40 can be suppressed.

Next, a method for manufacturing the fuel cell stack 10 of this embodiment will be described.

Figure 6 is a diagram explaining each step in the manufacturing method of the fuel cell stack 10.

First, as shown in FIG. 6(a), a fuel leakage prevention film 44 is formed on the metal support layer 22 of the cell unit 20. More specifically, a plurality of fuel leakage prevention films 44 (two in FIG. 6) are formed on the second surface 22b of the metal support layer 22 while leaving a space S extending in the electrode width direction X between each of the fuel leakage prevention films 44 for inserting the protrusions 30c of the separator 30. In particular, the fuel leakage prevention film 44 is formed by screen printing the raw material slurry on the second surface 22b of the metal support layer 22 and then drying it.

Next, as shown in FIG. 6(b), the first reforming catalyst layer 40 is applied to the second surface 22b of the metal support layer 22 so that its end 41 overlaps the fuel leakage prevention film 44. More specifically, the raw material slurry of the first reforming catalyst layer 40 is screen-printed on the second surface 22b of the metal support layer 22 while masking to form the end 41 that overlaps with the fuel leakage prevention film 44, and then dried by high-temperature treatment. Note that this high-temperature treatment causes the fuel leakage prevention film 44 to flow and adhere more favorably to the first reforming catalyst layer 40 and the second surface 22b of the metal support layer 22. Therefore, the fuel leakage prevention film 44 is filled so as to fill the gap that can be a gas passage from the fuel gas flow path 32 to the second surface 22b of the metal support layer 22. That is, the sealing function of the fuel leakage prevention film 44 against the leakage of fuel gas to the metal support layer 22 is more favorably secured.

Next, as shown in FIG. 6(c), the separator 30 is placed on the metal support layer 22. More specifically, the separator 30 is positioned so that the protrusions 30c formed on the first surface 30a of the separator 30 enter the spaces S between the adjacent fuel outflow prevention films 44 and abut against the second surface 22b of the metal support layer 22.

Then, as shown in FIG. 6(d), the contact portion Cp between the protrusion 30c of the separator 30 and the second surface 22b of the metal support layer 22 is laser-welded to join the separator 30 to the metal support layer 22.

In particular, in this embodiment, the protrusions 30c are formed on the first surface 30a of the separator 30, so that the contact area Cp between the separator 30 and the metal support layer 22 can be made to have a certain area or more, thereby reducing the amount of heat input during welding. In addition, due to the shape of the protrusions 30c, the separator 30 is joined to the metal support layer 22 in a state in which the first reforming catalyst layer 40 is pressed against the second surface 22b of the metal support layer 22. This makes it possible to more stably fix the first reforming catalyst layer 40 to the metal support layer 22.

The steps shown in Figures 6(a) to 6(d) above can be repeated a predetermined number of times according to the number of stacked cells included in the fuel cell stack 10 to form a fuel cell stack 10 in which multiple cell units 20 are stacked.

The configuration of the fuel cell stack 10 of this embodiment and the associated effects will now be described.

The fuel cell stack 10 of this embodiment includes an internal reforming type (particularly a direct internal reforming type) fuel cell (cell unit 20) in which the electrode layer (anode electrode layer 24 and cathode electrode layer 28) and the electrolyte layer 26 are supported on one surface (first surface 22a) of the metal support layer 22 and a separator 30 is attached to the other surface (second surface 22b), and is configured as a fuel cell structure in which a fuel flow path (fuel gas flow path 32) is formed in the space between the second surface 22b of the metal support layer 22 and the surface (first surface 30a) of the separator 30.

This fuel cell stack 10 comprises a first reforming catalyst layer 40 provided on the second surface 22b of the metal support layer 22 in the upstream region _Au of the fuel gas flow path 32, a second reforming catalyst layer 42 provided on the second surface 22b of the metal support layer 22 in the downstream region _Ad of the fuel gas flow path 32, and a fuel outflow prevention membrane 44 provided at an end 41 of the first reforming catalyst layer 40 in the gas flow direction Y of the fuel gas flow path 32 and which prevents fuel gas from bypassing the first reforming catalyst layer 40 and outflowing to the metal support layer 22.

In this fuel cell stack 10, the first reforming catalyst layer 40 is made of a material that is more effective at suppressing carbon deposition caused by the reforming reaction than the second reforming catalyst layer 42. Furthermore, the fuel outflow prevention film 44 includes a carbon oxide absorbent that absorbs carbon oxides (CO or _CO2 ) generated by the reforming reaction in the first reforming catalyst layer 40.

As a result, the first reforming catalyst layer 40 suppresses carbon deposition in the upstream region _Au of the fuel gas flow passage 32 where water produced by power generation is insufficient and carbon deposition is likely to occur, while the second reforming catalyst layer 42 ensures the efficiency of the reforming reaction in the downstream region _Ad where water produced by power generation is abundant. Furthermore, the fuel outflow prevention film 44 prevents the fuel gas from flowing out to the metal support layer 22 through a gap that may occur at the end 41 of the first reforming catalyst layer 40, and can absorb carbon oxides produced by the reforming reaction in the first reforming catalyst layer 40. Therefore, it is possible to suppress both carbon deposition in the upstream region _Au of the fuel gas flow passage 32 where water produced by power generation is relatively small, and catalyst deterioration caused by contact between carbon oxides produced by the reforming reaction in the first reforming catalyst layer 40 and the catalyst material.

In addition, in the fuel cell stack 10 of this embodiment, the first reforming catalyst layer 40 is configured by supporting catalyst particles 40b on a support (catalyst support 40a) configured of an oxide. In particular, the catalyst support 40a is configured of a material selected from the group consisting of metal oxides such as barium oxide (BaO), magnesium oxide (MgO), or calcium oxide (CaO), a mixture of one or more of the metal oxides, and solid solutions thereof. In addition, the catalyst particles 40b are fine particles (particularly nanoparticles) configured of a material selected from the group consisting of transition metals such as iron (Fe), nickel (Ni), cobalt (Co), or copper (Cu), rare earth elements such as lanthanum (La), precious metals such as ruthenium (Ru), platinum (Pt), rhodium (Rh), iridium (Ir), silver (Ag), or palladium (Pd), and a mixture of one or more of the above.

This makes it possible to effectively achieve the high carbon deposition suppression effect required for the first reforming catalyst layer 40.

In addition, in the fuel cell stack 10 of this embodiment, the end 41 of the first reforming catalyst layer 40 is configured to overlap the fuel outflow prevention film 44 in the stacking direction Z.

As a result, the end 41 of the first reforming catalyst layer 40 acts to block the inflow of the fuel outflow prevention film 44 into the inside of the first reforming catalyst layer 40, thereby suppressing the deterioration of catalyst performance caused by the fuel outflow prevention film 44 blocking the pores of the first reforming catalyst layer 40.

Furthermore, in this embodiment, a manufacturing method for manufacturing the fuel cell stack 10 is provided. This manufacturing method includes a step of applying a fuel outflow prevention film 44 to the surface of the metal support layer 22 in the fuel cell (cell unit 20) (FIG. 6(a)), a step of applying a first reforming catalyst layer 40 to the second surface 22b of the metal support layer 22 (FIG. 6(b)), a step of placing a separator 30 on the second surface 22b of the metal support layer 22 (FIG. 6(c)), and a step of laser welding the separator 30 and the second surface 22b of the metal support layer 22 (FIG. 6(d)).

This provides a suitable method for manufacturing a fuel cell stack 10 having the above configuration.

Second Embodiment
The second embodiment will be described below, in which the same elements as those in the first embodiment are given the same reference numerals and the description thereof will be omitted.

Figure 7A is a diagram illustrating the configuration of the fuel cell stack 10 according to this embodiment. In particular, Figure 7A(a) is a schematic side view of the fuel cell stack 10, and Figure 7A(b) is a schematic cross-sectional view of the fuel cell stack 10. Also, Figure 7B is a partially enlarged view of Figure 7A(b).

As shown in the figure, in the fuel cell stack 10 of this embodiment, a carbon deposition suppression catalyst layer 52 is provided over substantially the entire area of the first surface 30a of the separator 30 that faces the second surface 22b of the metal support layer 22.

This carbon deposition suppression catalyst layer 52, like the first reforming catalyst layer 40, is made of a material that is highly effective in suppressing carbon deposition caused by the reforming reaction. That is, the carbon deposition suppression catalyst layer 52 is made by supporting catalyst particles on a carrier made of an oxide.

In particular, the carrier constituting the carbon deposition suppression catalyst layer 52 is composed of a material selected from the group consisting of metal oxides such as barium oxide (BaO), magnesium oxide (MgO), or calcium oxide (CaO), a mixture of one or more of these metal oxides, and solid solutions thereof.

The catalyst particles are fine particles (particularly nanoparticles) made of a material selected from the group consisting of transition metals such as iron (Fe), nickel (Ni), cobalt (Co), or copper (Cu), rare earth elements such as lanthanum (La), precious metals such as ruthenium (Ru), platinum (Pt), rhodium (Rh), iridium (Ir), silver (Ag), or palladium (Pd), and mixtures of one or more of these.

From a manufacturing standpoint, it is preferable that the carbon deposition suppression catalyst layer 52 be made of the same material as the first reforming catalyst layer 40.

Furthermore, in the fuel cell stack 10 of this embodiment, a carbon oxide absorbing layer 54 is provided between the first surface 30a of the separator 30 and the carbon deposition suppression catalyst layer 52, over substantially the entire area of the first surface 30a of the separator 30.

The carbon oxide absorbing layer 54, like the fuel outflow prevention film 44, is made of a carbon oxide absorbing material that has a certain degree of thermal fluidity and absorbs carbon oxides (CO or _CO2 ). In particular, the carbon deposition prevention catalyst layer 52 is made by supporting catalyst particles on a carrier made of an oxide. More specifically, examples of the carbon oxide absorbing material that constitutes the carbon deposition prevention catalyst layer 52 include alkali metals or alkaline earth metals such as barium (Ba), calcium (Ca), or magnesium (Mg).

From a manufacturing standpoint, it is preferable that the carbon oxide absorbing layer 54 be made of the same material as the fuel outflow prevention film 44.

The carbon oxide absorbing layer 54 and the carbon deposition suppression catalyst layer 52 described above are applied in this order to the first surface 30a of the separator 30 by a coating method such as screen printing. That is, a composite layer consisting of the carbon oxide absorbing layer 54 and the carbon deposition suppression catalyst layer 52 is formed on the first surface 30a of the separator 30. The technical significance of this configuration is explained below.

As already explained, the separator 30 is made of a conductive metal material (particularly a transition metal material) such as Fe or Cr, and is therefore highly reactive to carbon, similar to the metal support layer 22. Therefore, it is expected that carbon generated by the reforming reaction in the first reforming catalyst layer 40 will come into contact with the first surface 30a of the separator 30, causing carbon deposition on the first surface 30a.

In contrast, in this embodiment, a carbon deposition suppression catalyst layer 52 is provided on the first surface 30a of the separator 30, thereby suppressing carbon deposition in the separator 30. Furthermore, a carbon oxide absorption layer 54 is provided on substantially the entire first surface 30a of the separator 30, so that the carbon oxides generated in the reforming reaction are absorbed by the carbon oxide absorption layer 54, thereby suppressing deterioration of the carbon deposition suppression catalyst layer 52.

In particular, in this embodiment, the carbon deposition suppression catalyst layer 52 is provided over substantially the entire area of the first surface 30a, so that the carbon deposition suppression catalyst layer 52 can effectively block carbon oxides that are guided in the direction toward the first reforming catalyst layer 40 by the curved shape of the separator 30. This makes it possible to more reliably prevent contact between the carbon oxides and the first reforming catalyst layer 40.

The configuration of the fuel cell stack 10 of this embodiment and the associated effects will now be described.

In the fuel cell stack 10 of this embodiment, the separator 30 is provided with a carbon deposition suppression catalyst layer 52 that is more effective at suppressing carbon deposition caused by the reforming reaction than the second reforming catalyst layer 42 over substantially the entire area of the first surface 30a that faces the metal support layer 22.

As a result, carbon generated in the first reforming catalyst layer 40 is blocked by the carbon deposition prevention catalyst layer 52, which has low reactivity with the carbon, so carbon deposition on the first surface 30a of the separator 30 can be more reliably prevented.

Furthermore, in this embodiment, the separator 30 is provided with a carbon oxide absorption layer 54 that absorbs carbon oxides between the first surface 30a of the separator 30 and the carbon deposition suppression catalyst layer 52.

As a result, the carbon oxides generated in the first reforming catalyst layer 40 are absorbed by the carbon oxide absorption layer 54, so that deterioration of the carbon deposition suppression catalyst layer 52 caused by the reaction between the carbon oxides and the carbon deposition suppression catalyst layer 52 can be effectively suppressed.

Below, we will explain each of the modified examples 1 to 3 that can be applied to the first embodiment or the second embodiment. Note that in each of Figures 8 to 10 for explaining modified examples 1 to 3, a fuel cell stack 10 is shown that is based on the configuration described in the first embodiment (the configuration shown in Figure 3, etc.). However, this is not intended to limit the configuration of each of the modified examples 1 to 3 to the configuration of the fuel cell stack 10 of the first embodiment. In other words, a fuel cell stack 10 that uses the configuration described in the second embodiment as a basic configuration and adopts at least one of the configurations of modified examples 1 to 3 is also included in the scope of what is disclosed in this specification, etc.

(Variation 1)
FIG. 8 is a diagram for explaining the configuration of the fuel cell stack 10 according to the first modification. As shown in the figure, in the fuel cell stack 10 according to the first modification, among the multiple (three in FIG. 8) fuel gas flow paths 32-1, 32-2, 32-3 arranged along the electrode width direction X, the first reforming catalyst layers 40-1, 40-3 provided in the fuel gas flow paths 32-1, 32-3 on the outer side in the width direction are formed thicker in the stacking direction Z than the first reforming catalyst layer 40-2 provided in the fuel gas flow path 32-2 on the inner side in the width direction. More specifically, the first reforming catalyst layers 40-1, 40-3 are configured so that the amount of catalyst particles 40b-1, 40b-3 supported on the catalyst carriers 40a-1, 40a-3 is larger than the amount of catalyst particles 40b-2 supported on the catalyst carrier 40a-2. The technical significance of this configuration will be explained.

In the direct internal reforming type fuel cell stack 10, the inside in the width direction where the electrochemical reaction (exothermic reaction) during power generation occurs more actively becomes relatively hot, and the outside in the width direction where it does not occur becomes relatively cold. That is, a temperature distribution occurs in the plane constituting the power generation area of the cell unit 20 due to the temperature difference between the inside in the width direction and the outside in the width direction. The occurrence of this temperature distribution causes variation in the viscosity of the fuel gas in the plane of the cell unit 20. Therefore, based on the temperature dependence characteristic of the viscosity of gas, the viscosity of the fuel gas in the inside in the width direction where the temperature is high is higher than that in the outside in the width direction where the temperature is low. For this reason, the fuel gas flow rate in the fuel gas flow path 32-2 on the inside in the width direction where the temperature is high becomes relatively small, and the fuel gas flow rate in the fuel gas flow paths 32-1, 32-3 on the outside in the width direction where the temperature is low becomes relatively large. As a result, carbon deposition is likely to occur on the outside in the width direction of the cell unit 20. In contrast, in the configuration of the modified example 1 shown in FIG. 8, the first reforming catalyst layers 40-1, 40-3 arranged on the outside in the width direction are configured to be thicker than the first reforming catalyst layer 40-2 arranged on the inside in the width direction. That is, the carbon deposition suppression effect of the first reforming catalyst layers 40-1 and 40-3 is improved compared to the first reforming catalyst layer 40-2, so carbon deposition can be more reliably suppressed on the outer side in the width direction where the fuel gas flow rate is greater.

(Variation 2)
In Modification 2, another aspect of one step of the manufacturing method for the fuel cell stack 10 described in Fig. 6 is provided. Specifically, in the manufacturing method of Modification 2, the step of welding the separator 30 to the metal support layer 22 (see Fig. 6(d)) is performed such that the amount of heat input to the welding in the upstream region _Au of the fuel gas flow field 32 is greater than the amount of heat input to the downstream region _Ad . The technical significance of performing the step in this manner will be described.

In the upstream region _Au of the fuel gas flow field 32, where the water generated by power generation is likely to be insufficient, carbon deposition is more likely to occur than in the downstream region _Ad . On the other hand, in the downstream region _Ad of the fuel gas flow field 32, the water generated by power generation is relatively abundant, and the generated water inhibits the occurrence of reactions that cause carbon deposition. Therefore, in the upstream region _Au , where carbon deposition is more likely to occur, it is desirable to employ a configuration that more reliably avoids contact between the fuel gas and the metal support layer 22 than in the downstream region _Ad , where carbon deposition is not likely to occur.

In response to such demands, in the second modification, in the process of welding the separator 30 to the metal support layer 22, the amount of heat input in the upstream region _Au of the fuel gas flow field 32 is made larger than the amount of heat input in the downstream region _Ad , thereby obtaining the fuel cell stack 10 having the configuration shown in FIG.

9, the weld bead 46u in the upstream region _Au is thicker than the weld bead 46d in the downstream region _Ad . This allows the thick weld bead 46u to more reliably block the path of fuel gas to the metal support layer 22 in the upstream region _Au . On the other hand, the weld bead 46d is relatively thin in the downstream region _Ad , where the requirement for blocking fuel gas is lower than in the upstream region _Au , so that the weld bead 46d can maintain the design accuracy of the fuel gas flow path 32.

(Variation 3)
Fig. 10 is a diagram illustrating the configuration of a fuel cell stack 10 according to Modification 3. As shown in the figure, in Modification 3, a separator 30 having a shape different from that of the separator 30 shown in Fig. 3 and the like is adopted from the viewpoint of further improving the springiness of the separator 30. This makes it possible to further improve the bonding strength between the separator 30 and the metal support layer 22. Note that, even if the shape is other than that shown in Fig. 10, any shape that can improve the springiness can be adopted as long as the original function of the separator 30 can be ensured.

Although each embodiment of the present invention has been described above, the above embodiments merely show some of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments.

Furthermore, the above embodiments and variations can be combined in any manner as long as they are not mutually inconsistent.

REFERENCE SIGNS LIST 10 fuel cell stack 20 cell unit 22 metal support layer 24 anode electrode layer 26 electrolyte layer 28 cathode electrode layer 30 separator 30a first surface 30b second surface 30c protrusion 32 fuel gas flow path 34 oxidant gas flow path 40 first reforming catalyst layer 41 both ends 42 second reforming catalyst layer 44 fuel outflow prevention film 52 carbon deposition suppression catalyst layer 54 carbon oxide absorbing layer

Claims (6)

A fuel cell structure including an internal reforming type fuel cell in which an electrode layer and an electrolyte layer are supported on one surface of a metal support layer and a separator is attached to the other surface of the metal support layer, and a fuel flow path is formed in a space between the other surface of the metal support layer and a surface of the separator,
a first reforming catalyst layer provided on the other surface of the metal support layer in the upstream region of the fuel flow channel , the first reforming catalyst layer extending over a predetermined range in a gas flow direction of the fuel flow channel and in an electrode width direction perpendicular to the gas flow direction ;
a second reforming catalyst layer provided on the other surface of the metal support layer in a downstream region of the fuel flow channel;
a fuel outflow prevention film provided at an end of the first reforming catalyst layer in the electrode width direction and configured to prevent fuel from bypassing the first reforming catalyst layer and outflowing to the metal support layer;
Equipped with
the first reforming catalyst layer is made of a material that is more effective in suppressing carbon deposition caused by a reforming reaction than the second reforming catalyst layer;
the fuel outflow prevention film includes a carbon oxide absorbent that absorbs carbon oxides generated by the reforming reaction in the first reforming catalyst layer.
Fuel cell structure. 2. The fuel cell structure according to claim 1,
The first reforming catalyst layer is configured by supporting catalyst particles on a support made of an oxide.
Fuel cell structure. 3. The fuel cell structure according to claim 1 or 2,
an end portion of the first reforming catalyst layer is configured to overlap with the fuel outflow prevention film in the stacking direction;
Fuel cell structure. The fuel cell structure according to any one of claims 1 to 3,
the separator is provided with a carbon deposition suppression catalyst layer that is more effective at suppressing carbon deposition caused by the reforming reaction than the second reforming catalyst layer over substantially the entire surface of the separator;
Fuel cell structure. The fuel cell structure according to claim 4,
The separator has a carbon oxide absorbing layer between a surface of the separator and the carbon deposition suppression catalyst layer, the carbon oxide absorbing layer absorbing carbon oxides.
Fuel cell structure. A method for manufacturing the fuel cell structure according to any one of claims 1 to 5, comprising the steps of:
applying the fuel outflow prevention film to the other surface of the metal support layer in the fuel cell;
applying the first reforming catalyst layer to the other side of the metal support layer;
disposing the separator on a surface of the metal support layer;
and laser welding the separator and the surface of the metal support layer.
A method for manufacturing a fuel cell structure.

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