JP2009087809A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology capable of improving a temperature distribution inside a fuel cell during power generation. <P>SOLUTION: The fuel cell 100 is supplied with a fuel gas containing hydrogen and a hydrocarbon compound. The fuel cell 100 is provided with a membrane electrode assembly 10 including an electrolyte membrane 11 pinched by an anode 12 and a cathode 13, and a fuel gas passage 21 for the fuel gas which is installed on the anode side electrode face of the membrane electrode assembly 10. In the fuel gas passage 21, a shift catalyst layer 41 for promoting a shift reaction of the hydrocarbon compound and a reforming catalyst layer 40 for promoting a reforming reaction of the hydrocarbon compound are laminated, and the shift catalyst layer 41 is arranged at a position nearer to the anode 12 than the reforming catalyst layer 40. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell.

  In a fuel cell, in order to improve the power generation efficiency, it is desirable to make the temperature distribution in the power generation region used for power generation uniform. Various techniques for making the temperature distribution in the power generation region uniform have been proposed (Patent Document 1, etc.).

JP 2005-190684 A JP 2004-273343 A

  By the way, in order to continue the fuel cell reaction satisfactorily, it is preferable that a predetermined temperature (for example, about 80 ° C.) is maintained in the power generation region. However, on the other hand, when viewed as a whole fuel cell, it is desired that the operating temperature of the fuel cell be lower. As described above, it has been desired to improve the temperature distribution inside the fuel cell during power generation. However, until now, it has been the actual situation that no sufficient contrivance has been made for such demand.

  An object of this invention is to provide the technique which can improve the temperature distribution inside the fuel cell under electric power generation.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

Application Example 1 A fuel cell to which a fuel gas containing hydrogen and a hydrocarbon-based hydrogen compound is supplied, the membrane electrode assembly including an electrolyte membrane sandwiched between an anode and a cathode, and the anode of the membrane electrode assembly A fuel gas flow path for the fuel gas provided on a side electrode surface, the fuel gas flow path including a shift catalyst layer for promoting a shift reaction of the hydrocarbon-based hydrogen compound, and the carbonization And a reforming catalyst layer for promoting a reforming reaction of the hydrogen compound, and the shift catalyst layer is disposed closer to the anode than the reforming catalyst layer. According to this fuel cell, it is possible to reduce the operating temperature when viewed as the whole fuel cell by the endothermic reaction in the reforming catalyst layer while maintaining the temperature of the power generation region at a relatively high temperature by the exothermic reaction in the shift catalyst layer. Is possible. Further, the shift catalyst layer can buffer the cooling effect on the power generation region due to the endothermic reaction of the reforming catalyst layer. Therefore, the temperature distribution inside the fuel cell during power generation can be improved.

Application Example 2 The fuel cell according to Application Example 1, wherein the anode includes a hydrogen-permeable metal that selectively permeates hydrogen. According to this fuel cell, the temperature distribution inside the fuel cell in the hydrogen separation membrane fuel cell during power generation can be improved.

[Application Example 3] The fuel cell according to Application Example 1 or Application Example 2, wherein the ratio of the content of the reforming catalyst contained in the reforming catalyst layer to the content of the shift catalyst contained in the shift catalyst layer The catalyst content ratio is a fuel cell that becomes larger toward the downstream side of the fuel gas passage. According to this fuel cell, the cooling effect by the endothermic reaction in the reforming catalyst layer can be reduced toward the upstream side of the fuel gas. Accordingly, the temperature distribution in the power generation region can be made more uniform.

Application Example 4 The fuel cell according to Application Example 1 or Application Example 2, wherein the ratio of the content of the reforming catalyst contained in the reforming catalyst layer to the content of the shift catalyst contained in the shift catalyst layer The catalyst content ratio is a fuel cell that increases as the temperature of the fuel gas flow path increases when the fuel cell is continuously operated. According to this fuel cell, the cooling effect by the reforming catalyst layer can be increased in the region where the temperature is higher in the power generation region when the fuel cell is continuously operated. Accordingly, the temperature distribution in the power generation region can be made more uniform.

  The present invention can be realized in various forms, for example, in the form of a fuel cell, a fuel cell system including the fuel cell, a vehicle equipped with the fuel cell system, and the like. .

A. First embodiment:
FIG. 1 is a schematic sectional view showing the structure of a fuel cell as one embodiment of the present invention. This fuel cell 100 is a so-called hydrogen separation membrane fuel cell including a hydrogen separation membrane that can selectively permeate hydrogen in fuel gas supplied to the anode side. The fuel cell 100 does not have to be a hydrogen separation membrane fuel cell. For example, the present invention can be applied to other solid oxide fuel cells.

  The fuel cell 100 has a so-called stack structure in which a plurality of power generation modules 110 that are power generation bodies are stacked. The power generation module 110 includes a membrane electrode assembly 10 and separators 20 and 30 that sandwich the membrane electrode assembly 10. The membrane electrode assembly 10 includes an electrolyte membrane 11 sandwiched between an anode 12 and a cathode 13.

The electrolyte membrane 11 can be made of, for example, BaCeO ₃ or SrCeO ₃ ceramic proton conductor. The anode 12 can be composed of a metal thin film having hydrogen permeability such as palladium (Pd) or a palladium alloy. Thus, the anode 12 can selectively permeate only hydrogen from the gas flow path 21 to the electrolyte membrane 11A side.

  The cathode 13 has a catalyst layer (not shown) for promoting a power generation reaction on the outer surface in contact with the electrolyte membrane 11, and the supplied oxidizing gas is spread all over the outer surface not in contact with the electrolyte membrane 11. A gas diffusion layer (not shown) is provided. In the following, in this specification, a region for power generation including the electrolyte membrane 11 and the two electrodes 12 and 13 of the fuel cell 100 is referred to as a “power generation region”.

  Separator 20,30 can be comprised with the gas-impermeable plate-shaped member (for example, metal plate) which has electroconductivity. Gas flow paths 21 and 31 for guiding the fuel gas and the oxidizing gas (reactive gas) are provided on the side of the separators 20 and 30 that are in contact with the electrodes 12 and 13, respectively. The gas flow paths 21 and 31 are configured as a plurality of flow path grooves that run along the outer surfaces of the separators 20 and 30 over the entire power generation region. Note that a refrigerant flow path for guiding the refrigerant is provided on the outer surface of the separators 20 and 30 that does not contact the electrodes 12 and 13 (not shown).

  In the gas flow path 21 of the anode separator 20 disposed on the anode side, a reforming catalyst layer 40 supporting a reforming catalyst and a shift catalyst layer 41 supporting a shift catalyst are used as anodes for the shift catalyst layer 41. Laminated as the 12th side.

  The reforming catalyst is a catalyst for promoting a reforming reaction described later. As the reforming catalyst, for example, rhodium (Rh), ruthenium (Ru), platinum (Pt), nickel (Ni) or the like can be employed. The shift catalyst is a catalyst for promoting a shift reaction described later. As the shift catalyst, for example, copper (Cu), iron (Fe), palladium (Pd), or the like can be employed.

  These two catalyst layers 40 and 41 are subjected to temporary firing after applying the slurryed reforming catalyst to the outer surface of the gas flow path 21 of the anode separator 20, and further, the slurryed shift catalyst is stacked thereon. It can provide by performing this baking after apply | coating.

  By the way, the fuel gas of the fuel cell 100 of the present embodiment is supplied with a hydrocarbon-based compound as a raw material, undergoing a reforming reaction / shift reaction in a reformer and purified as a hydrogen-rich gas. The raw material hydrocarbon compound includes, for example, methanol, natural gas, gasoline, dimethyl ether, acetaldehyde and the like.

In general, the fuel gas purified by the reformer contains methane (CH ₄ ) and carbon monoxide (CO) along with hydrogen according to the reaction temperature in the reformer. In this fuel cell 100, since the reforming catalyst layer 40 is provided in the gas flow path 21, the reforming for purifying hydrogen (H ₂ ) and carbon monoxide from methane and water vapor (H ₂ 0) in the fuel gas. The quality reaction is promoted (reaction formula (1)).
CH ₄ + H ₂ 0 → 3H ₂ + CO (1)

In addition, since the shift catalyst layer 41 is provided in the gas flow path 21, a shift reaction in which hydrogen and carbon dioxide (CO ₂ ) are generated from carbon monoxide and water vapor is promoted (reaction formula ( 2)).
CO + H ₂ 0 → H ₂ + CO ₂ (2)

  In general, the reforming reaction and shift reaction shown in the above reaction formulas (1) and (2) are equilibrium reactions. However, on the anode side of the fuel cell 100 during power generation, hydrogen is supplied to and consumed in the power generation reaction, so that both the two reactions generate hydrogen according to the amount of hydrogen consumption on the anode side (reaction). Proceed in the direction of the arrow going from the left side of the expression to the right side).

  Here, since carbon monoxide is toxic, the fuel cell may be deteriorated due to the carbon monoxide present on the anode side. Carbon monoxide can be consumed by the shift reaction, but the shift reaction has a slower reaction rate than the reforming reaction that produces carbon monoxide. Therefore, in this fuel cell 100, by providing the shift catalyst layer 41 at a position closer to the anode 12 where more hydrogen is consumed by the power generation reaction, the shift reaction proceeds in the direction of carbon monoxide consumption and hydrogen generation. To promote.

  The reforming reaction is an endothermic reaction when the reaction proceeds in the direction of hydrogen generation. That is, when the amount of hydrogen consumed by the power generation reaction increases and the amount of heat generated increases, the reforming reaction proceeds in the direction of increasing the endothermic amount. Therefore, the reforming catalyst layer 40 can serve as a cooling unit for suppressing the fuel cell from becoming higher than a predetermined operating temperature due to heat generated by the power generation reaction.

  By the way, assuming that the reforming catalyst layer 40 is provided directly adjacent to the anode 12, the power generation region is excessively cooled by the cooling function of the reforming catalyst layer 40. It may hinder and reduce power generation efficiency. However, since the shift catalyst layer 41 is provided between the anode 12 and the reforming catalyst layer 40 in the fuel cell 100 of the present embodiment, the shift catalyst layer 41 is located between the anode 12 and the reforming catalyst layer 40. The heat transfer is buffered, and excessive temperature drop in the power generation area is suppressed. That is, the shift catalyst layer 41 functions as a heat transfer buffer material.

  In contrast to the reforming reaction, the shift reaction becomes an exothermic reaction when the reaction proceeds in the hydrogen generation direction. That is, the power generation module 110 is kept at a relatively high temperature by the reaction heat generated by the power generation reaction and the heat from the shift catalyst layer 41 as the power generation region is closer to the power generation region. It is kept relatively cool by the road. Therefore, the fuel cell 100 can continue to operate at a relatively low temperature when viewed as a whole fuel cell while maintaining the power generation region at a high temperature that allows the power generation reaction to continue satisfactorily.

  In general, a hydrogen separation membrane fuel cell such as the fuel cell 100 of this embodiment has an operating temperature as high as 400 to 600 ° C. Therefore, during the power generation of the fuel cell 100, the reforming catalyst and the shift catalyst exhibit high activity, and thus the above-described effects can be obtained more highly.

  As described above, in the fuel cell 100 of the present embodiment, the reforming catalyst layer 40 and the shift catalyst layer 41 are stacked in the gas flow path 21 on the anode side, and the shift catalyst layer 41 is formed from the reforming catalyst layer 40. Is also located closer to the anode 12. With this configuration, the temperature distribution inside the fuel cell 100 during power generation can be improved.

B. Second embodiment:
FIG. 2 is a schematic sectional view showing the structure of a fuel cell 100A as a second embodiment of the present invention. FIG. 2 is substantially the same as FIG. 1 except that the electrolyte membrane 11A and the anode 12A having different constituent members are used instead of the electrolyte membrane 11 and the anode 12.

  The electrolyte membrane 11A of the fuel cell 100A is a solid polymer that exhibits good proton conductivity in a wet state. Similarly to the cathode 13, the anode 12A is configured to have a catalyst layer and a gas diffusion layer. That is, the fuel cell 100A is a so-called solid polymer fuel cell. Here, the operating temperature of the polymer electrolyte fuel cell is generally about 80 ° C. Thus, the present invention can be applied not only to the hydrogen separation membrane fuel cell as in the first embodiment but also to various types of fuel cells having different operating temperatures.

C. Third embodiment:
FIG. 3A is a schematic diagram showing the configuration of an anode separator 20A used in a fuel cell as a third embodiment of the present invention. FIG. 3 (A) shows the surface side of the anode separator 20 shown in FIG. 1 where the gas flow path 21 is provided. The reforming catalyst is provided in the gas flow path 21 as in the first embodiment. A layer 40 and a shift catalyst layer 41 are provided. The other configuration of the fuel cell of the present embodiment is the same as that of the fuel cell 100 of the first embodiment except for the separator 20A.

  The separator 20A is provided with manifolds M1 to M6 for the reaction gas and the refrigerant as through holes. Specifically, the fuel gas supply manifold M1 and the discharge manifold M2 are provided at positions facing each other with the gas flow path 21 therebetween. Similarly, oxidant gas and refrigerant supply manifolds M3 and M5 and oxidant gas and refrigerant discharge manifolds M4 and M6 are provided at positions facing each other across the gas flow path 21, respectively.

  Each flow channel of the gas flow channel 21 runs side by side from the fuel gas supply manifold M1 side toward the discharge manifold M2 side. Further, the separator 20 is provided with a connection gas flow path 24 that is connected to each flow path groove of the gas flow path 21 and is connected to the fuel gas supply manifold M1 or the discharge manifold M2.

  As a result, the fuel gas flows in the power generation region from the supply manifold M1 to the discharge manifold M2 via the connection gas flow path 24 and the gas flow path 21 as indicated by the arrows in the figure. Hereinafter, the direction in which the fuel gas flows in this power generation region (X-axis direction in the figure) is referred to as the “gas flow path direction”.

  FIG. 3B is a graph showing the relationship between the distance in the gas flow path direction of the gas flow path 21 and the catalyst content ratio in the power generation region. Here, the “catalyst content ratio” is the ratio (Mr) of the content (Mr) of the reforming catalyst contained in the reforming catalyst layer 40 to the content (Ms) of the shift catalyst contained in the shift catalyst layer 41. / Ms).

  As can be understood from this graph, in this separator 20A, the catalyst content ratio increases as it approaches the supply manifold M1 from the discharge manifold M2, that is, the downstream side of the gas flow path 21. This means that the content Mr of the reforming catalyst increases with respect to the content Ms of the shift catalyst toward the downstream side of the gas flow path 21.

  As described in the first example, the reforming reaction has a higher reaction rate than the shift reaction. Further, the upstream side of the gas passage 21 contains more methane in the fuel gas, and the reforming reaction proceeds in the endothermic direction according to the amount. Therefore, if the catalyst content ratio is constant in the gas flow path direction, the amount of heat absorbed by the reforming reaction increases toward the upstream side, and the temperature distribution in the power generation region during power generation becomes uneven. Generally, the power generation efficiency of the fuel cell decreases as the temperature distribution in the power generation region during power generation becomes more uneven.

  On the other hand, according to the separator 20A of the third embodiment, the amount of the reforming catalyst content Mr with respect to the shift catalyst content Ms is smaller toward the upstream side of the gas flow path 21, and therefore, the upstream side reforming catalyst layer 40. The amount of heat absorbed by is reduced accordingly, and the temperature distribution in the power generation region is made more uniform.

  Thus, according to the configuration of the third embodiment, the temperature distribution inside the fuel cell during power generation is further improved by adjusting the loading amounts of the reforming catalyst and the shift catalyst according to the flow direction of the reaction gas. Is possible.

D. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

D1. Modification 1:
In the above-described embodiment, the separators 20 and 30 are provided with the gas flow passages 21 and 31 as a plurality of parallel flow passage grooves, but the gas flow passages 21 and 31 are not necessarily provided as the flow passage grooves. good. For example, the gas flow paths 21 and 31 may be configured by a porous body disposed over the entire power generation region. In this case, the reforming catalyst layer 40 and the shift catalyst layer 41 may be provided over the entire power generation region.

D2. Modification 2:
In the third embodiment, the catalyst content ratio is linearly increased along the gas flow path direction. However, the catalyst content ratio can be arbitrarily increased or decreased for each region in the power generation region. For example, the catalyst content ratio may be increased or decreased according to the temperature distribution in the power generation region of the fuel cell. Specifically, when power generation is continued, the catalyst content ratio may be increased in a region where the temperature is predicted to increase, and the catalyst content ratio may be decreased in a region where the temperature is predicted to decrease.

  In addition, since the temperature distribution in the power generation region varies depending on various conditions in the design of the fuel cell, it is preferable to specifically examine them individually by analysis such as experiments. For example, in general, the temperature distribution in the power generation region of the fuel cell also varies depending on the flow direction of the fuel gas and the oxidizing gas. Therefore, when setting the catalyst content ratio, the catalyst content ratio may be increased or decreased not only according to the flow direction of the fuel gas but also according to the flow direction of the oxidizing gas. In general, since the cooling effect is smaller on the discharge side (downstream side) than on the refrigerant supply side (upstream side), the catalyst content ratio may be increased toward the downstream side of the refrigerant according to the difference in cooling effect. good.

  In general, in a fuel cell, it is preferable that the operating temperature of each power generation module (single cell) is uniform. Therefore, the temperature distribution of the entire fuel cell may be improved by adjusting the amount of catalyst supported on each catalyst layer for each power generation module to give a difference in cooling effect.

1 is a schematic cross-sectional view showing a configuration of a fuel cell according to a first embodiment. The schematic sectional drawing which shows the structure of the fuel cell of 2nd Example. The schematic which shows the flow of the fuel gas in the surface by the side of the anode of a separator, and the graph which shows the relationship between the position in a power generation area | region, and a catalyst content ratio.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Membrane electrode assembly 11, 11A ... Electrolyte membrane 12, 12A ... Anode 20, 20A, 30 ... Separator 21, 31 ... Gas flow path 24 ... Connection gas flow path 40 ... Reforming catalyst layer 41 ... Shift catalyst layer 100, 100A ... Fuel cell 110 ... Power generation module M1-M6 ... Manifold

Claims (4)

A fuel cell to which a fuel gas containing hydrogen and a hydrocarbon compound is supplied,
A membrane electrode assembly including an electrolyte membrane sandwiched between an anode and a cathode;
A fuel gas flow path for the fuel gas provided on the anode side electrode surface of the membrane electrode assembly;
With
In the fuel gas flow path, a shift catalyst layer for promoting a shift reaction of the hydrocarbon-based hydrogen compound and a reforming catalyst layer for promoting a reforming reaction of the hydrocarbon-based hydrogen compound are laminated. The fuel cell, wherein the shift catalyst layer is disposed closer to the anode than the reforming catalyst layer. The fuel cell according to claim 2, wherein
The anode is a fuel cell, comprising a hydrogen permeable metal that selectively permeates hydrogen. The fuel cell according to claim 1 or 2, wherein
The catalyst content ratio, which is the ratio of the content of the reforming catalyst contained in the reforming catalyst layer to the content of the shift catalyst contained in the shift catalyst layer, increases toward the downstream side of the fuel gas flow path. Fuel cell. The fuel cell according to claim 1 or 2, wherein
The catalyst content ratio, which is the ratio of the content of the reforming catalyst contained in the reforming catalyst layer to the content of the shift catalyst contained in the shift catalyst layer, is determined when the fuel cell is continuously operated. A fuel cell in which the temperature increases in the gas flow path.

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