JP2008152934A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell having separator structure superior in gas flow distribution, in the direction of cell inner face. <P>SOLUTION: In the fuel cell having a porous body layer as a gas passage, separator structure that is superior in gas flow distribution in the direction of cell inner face can be obtained, by increasing the width L1 of a common rail to be larger than the width of separator pores L2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell, and more particularly to a fuel cell including a porous layer as a gas flow path.

  As one of the countermeasures for environmental problems and resource problems, an electrochemical reaction using an oxidizing gas such as oxygen or air and a reducing gas such as hydrogen or methane (fuel gas) or a liquid fuel such as methanol as raw materials Fuel cells that generate electricity by converting chemical energy into electrical energy have attracted attention. The fuel cell is provided with a fuel electrode (anode catalyst layer) on one side of the electrolyte membrane and an air electrode (cathode catalyst layer) on the other side with the electrolyte membrane sandwiched therebetween, Further, a diffusion layer is further provided, and a single cell is configured by sandwiching these layers with a separator provided with a flow path for supplying raw materials. A plurality of single cells are stacked to form a fuel cell stack, and power is generated by supplying raw materials such as hydrogen and oxygen to each catalyst layer.

  At the time of power generation of the fuel cell, when hydrogen gas is used as the raw material supplied to the fuel electrode and air is used as the raw material supplied to the air electrode, hydrogen ions and electrons are generated from the hydrogen gas at the fuel electrode. The electrons reach the air electrode from the external terminal through the external circuit. In the air electrode, water is generated by oxygen in the supplied air, hydrogen ions that have passed through the electrolyte membrane, and electrons that have reached the air electrode through an external circuit. Thus, a chemical reaction occurs in the fuel electrode and the air electrode, and electric charges are generated to function as a battery. This fuel cell has been studied in various ways as a clean energy source due to the abundance of raw material gas and liquid fuel used for power generation and the fact that the substance discharged from the power generation principle is water. Has been.

  In a normal fuel cell, a reaction gas such as hydrogen gas and air (oxygen) is supplied from a supply path (manifold) of hydrogen gas and air through a reaction gas supply channel formed in a carbon or metal separator of each cell. And is supplied to a fuel electrode and an air electrode formed on both sides of the electrolyte membrane through a diffusion layer made of carbon cloth or carbon paper, and electricity is generated. However, when the reaction gas is supplied through the reaction gas supply channel formed in the separator, it is difficult to sufficiently diffuse (supply) the reaction gas in the cell in-plane direction. The output for each part may be non-uniform, and the power generation efficiency of the cell may be reduced.

  Therefore, instead of the reaction gas supply channel formed in the separator, a porous body layer is provided outside the diffusion layer, and the reaction gas can be uniformly supplied in the cell in-plane direction using the porous layer as the reaction gas supply channel. Proposed.

  A schematic top view of an example of a conventional configuration of a fuel cell for supplying a reaction gas through a porous layer is shown in FIGS. 11 and 11, and a C-C ′ cross section and a D-D ′ cross section in FIG. As shown in FIG. 12, the unit cell 5 of the fuel cell is formed such that the fuel electrode 102 is opposed to one surface of the electrolyte membrane 100 and the air electrode 104 is opposed to the other surface with the electrolyte membrane 100 interposed therebetween. A membrane electrode assembly (MEA) 110 having diffusion layers 106 and 108 provided on both sides of the catalyst layer (the fuel electrode 102 and the air electrode 104) is provided, and the porous body layer 112, 114 respectively. Furthermore, the anode side separator 116 and the cathode side separator 118 are outside the porous layers 112 and 114, and the anode side LLC separator 120 and the cathode side LLC separator 122 are outside the anode side separator 116 and the cathode side separator 118, respectively. Is provided. The anode side separator 116 is provided with an anode separator hole 124, the anode side LLC separator 120 is provided with an anode common rail 126 facing the anode separator hole 124, and the cathode side separator 118 is provided with a cathode separator hole 128. A cathode common rail 130 is provided on the LLC separator 122 so as to face the cathode separator hole 128.

  As shown in FIG. 11, hydrogen gas, which is a reaction gas, flows from the fuel gas manifold 132 through the anode common rail 126 through the communication passage 134 of the anode-side LLC separator 120 in the in-plane width direction, and from the anode common rail 126 to FIG. It is supplied to the porous body layer 112 through the anode separator hole 124 and supplied into the cell surface through the porous body layer 112 (see the arrow in FIG. 11). On the other hand, the used hydrogen gas is discharged through the porous body layer 112 through the anode separator hole 124, the anode common rail 126, the communication path 134, and the fuel gas manifold 132.

  Further, for example, Patent Document 1 describes a fuel cell in which reaction gas supply paths are evenly arranged in a cell surface and the reaction gas is supplied via a porous layer provided outside the diffusion layer. Yes. Patent Document 2 describes a fuel cell that includes a porous body layer outside a diffusion layer and is configured such that the porosity of the porous body layer decreases from the upstream to the downstream of the reaction gas flow path. Yes.

JP 2005-251432 A JP 2006-134582 A

  However, in the configuration shown in FIGS. 11 and 12, since the width of the anode common rail 126 is smaller than the width of the anode separator hole 124, the gas distribution in the cell in-plane direction is poor, and the gas flow rate is reduced particularly near the center of the cell. However, the gas flow rate increases on the gas inlet side and the outlet side, which causes a reduction in the power generation performance of the cell.

  Further, the methods of Patent Documents 1 and 2 have a problem that the configuration is complicated.

  The present invention is a fuel cell having a separator structure that is excellent in gas distribution in the cell in-plane direction.

  The present invention provides a membrane electrode assembly having an electrolyte membrane, a catalyst layer formed on both surfaces of the electrolyte membrane, and a diffusion layer formed on the surface of the catalyst layer, and a surface of the membrane electrode assembly. A porous body layer formed between the first separator having a separator hole for sandwiching the porous body layer and supplying a reaction gas in a width direction of the porous body layer, and sandwiching the first separator, And a second separator having a common rail provided oppositely, and the width of the common rail is larger than the width of the separator hole on at least one side of the catalyst layer.

  In the fuel cell, it is preferable that a width of the common rail is larger than a width of the separator hole on the anode side of the catalyst layer.

  The present invention provides a fuel cell having a separator structure with excellent gas distribution in the cell plane direction by making the width of the common rail larger than the width of the separator hole in a fuel cell having a porous layer as a gas flow path. be able to.

  Embodiments of the present invention will be described below. This embodiment is an example for carrying out the present invention, and the present invention is not limited to this embodiment.

<Fuel cell>
FIG. 1 shows a schematic side view of an example of a solid polymer electrolyte fuel cell 1 according to the present embodiment. FIG. 2 shows a schematic top view of an example of the single cell 3 in the fuel cell 1 according to the present embodiment, and FIG. 3 shows an AA ′ section and a BB ′ section in FIG. As shown in FIG. 3, each single cell 3 in FIG. 1 is composed of a laminate of MEA 20, porous layers 22 and 24, and separators 42 and 44.

  As shown in FIG. 3, each single cell 3 is formed such that the fuel electrode 12 is opposed to one surface of the electrolyte membrane 10 and the air electrode 14 is opposed to the other surface with the electrolyte membrane 10 interposed therebetween. A membrane electrode assembly (MEA) 20 having diffusion layers 16 and 18 provided on both sides of a layer (fuel electrode 12 and air electrode 14) is provided. Porous layers 22 and 24 are provided as reaction gas supply channels on both outer sides of the diffusion layers 16 and 18, respectively. Furthermore, an anode side separator 26 and a cathode side separator 28 which are first separators are provided outside the porous layers 22 and 24, and an anode side LLC which is a first separator is provided outside the anode side separators 26 and 28. A separator 30 and a cathode side LLC separator 32 are provided. The anode side separator 26 is provided with an anode separator hole 34, the anode side LLC separator 30 is provided with an anode common rail 36 so as to face the anode separator hole 34, and the cathode side separator 28 is provided with a cathode separator hole 38. A cathode common rail 40 is provided on the LLC separator 32 so as to face the cathode separator hole 38.

  As shown in FIG. 2, the single cell 3 has a power generation region 54 (inside the dotted line P in FIG. 2) in which a gas flow path, a refrigerant flow path, and an electrode exist in the center, and is located around the power generation area 54. A non-power generation region 56 that does not generate power is included. The non-power generation region 56 of the anode-side LLC separator 30 includes an inlet-side fuel gas manifold 46a that is a fuel gas supply path, an outlet-side fuel gas manifold 46b, an oxidizing gas supply path that is an inlet-side oxidizing gas manifold 50a, and an outlet. A side oxidizing gas manifold 50b, an inlet side refrigerant manifold 52a which is a refrigerant supply path, and an outlet side refrigerant manifold 52b are provided. In addition, an anode common rail 36a communicated with the fuel gas manifold 46a on the inlet side by the communication passage 48a is provided in the width direction at the end portion on the gas inlet side of the power generation region 54, and at the end portion on the gas outlet side, An anode common rail 36b communicated with the fuel gas manifold 46b through the communication passage 48b is provided in the width direction. Although not shown in FIG. 2, anode separator holes 34 a and 34 b are provided in the same width direction of the anode side separator 26 so as to face the anode common rails 36 a and 36 b. Refrigerant flow paths are formed on the opposite surfaces of the anode-side LLC separator 30 and the cathode-side LLC separator 32 that face the anode-side separator 26 and the cathode-side separator 28, respectively, but they are not shown. .

  3, porous layers 22 and 24 sandwiching both outer sides of diffusion layers 16 and 18 of MEA 20, anode side separator 26, cathode side separator 28, anode side LLC separator 30, cathode side LLC separator 32, As shown in FIG. 1, the single cells 3 are stacked to form a cell stacked body 58, and terminals 60, insulators 62, and end plates 64 are provided at both ends of the cell stacked body 58 in the cell stacking direction. The cell stack 58 is clamped in the cell stacking direction, and fixed by a fastening member (for example, a tension plate) 66, a bolt / nut 68, etc. extending outside the cell stack 58 in the cell stacking direction. 70 is configured. The number of single cells 3 in the cell stack 58 is not particularly limited as long as it is one or more.

  Normally, various fluids (fuel gas, oxidizing gas, refrigerant) flowing through the fuel gas manifolds 46a, 46b, the oxidizing gas manifolds 50a, 50b, and the refrigerant manifolds 52a, 52b are separated from each other and from the outside by a sealing material such as a gasket. These fluids are sealed. The sealing material is disposed around the power generation region 54 and around the manifold excluding the communication passages 48a and 48b.

  As shown in FIG. 2, fuel gas (usually hydrogen gas) flows from the fuel gas manifold 46a through the anode common rail 36a in the in-plane width direction via the communication passage 48a of the anode-side LLC separator 30, and from the anode common rail 36a to the membrane. 3 is supplied to the porous body layer 22 through the anode separator hole 34 in FIG. 3 in the thickness direction (cell stacking direction), and is supplied into the cell surface through the porous body layer 22 (see arrows in FIG. 2). On the other hand, the used hydrogen gas is discharged through the porous layer 22 through the anode separator hole 34, the anode common rail 36b, the communication passage 48b, and the fuel gas manifold 46b. The same applies to oxidizing gas (usually air).

  FIG. 4 shows an enlarged view within a dotted line Q in FIG. In the present embodiment, as shown in FIGS. 3 and 4, the width L1 of the anode common rail 36a is larger than the width L2 of the anode separator hole 34a (L1> L2). The same applies to the width L1 of the anode common rail 36b on the outlet side and the width L2 of the anode separator hole 34. As described above, when the width L1 of the anode common rail 36 is made larger than the width L2 of the anode separator hole 34 (L1> L2), the width L1 of the anode common rail 36 is equal to or smaller than the width L2 of the anode separator hole 34. Compared with (L1 ≦ L2), the gas distribution in the cell in-plane direction (direction substantially perpendicular to the cell stacking direction) is excellent.

  FIG. 5 shows an enlarged perspective view within a dotted line Q in FIG. According to the configuration of the present embodiment, when the width L1 of the anode common rail 36a is larger than the width L2 of the anode separator hole 34a on the gas inlet side, the width L1 of the anode common rail 36a is smaller than the width L2 of the anode separator hole 34a. In comparison, the pressure loss in the anode common rail 36a is reduced. Therefore, the reactive gas easily flows in the in-plane width direction (x direction in FIG. 5) through the anode common rail 36a via the communication path 48a, and after sufficiently flowing in the x direction, the film thickness direction (cell stacking direction, FIG. 5 in the z direction) to the porous layer 22 through the anode separator hole 34a.

  On the other hand, on the gas outlet side, as shown in FIG. 6 in an enlarged perspective view within the dotted line R in FIG. 2, the width L1 of the anode common rail 36b is larger than the width L2 of the anode separator hole 34b. The pressure loss in the anode common rail 36b is lower than when the width is smaller than the width L2 of the anode separator hole 34b. Therefore, the used reactive gas flows through the anode common rail 36b in the in-plane width direction (x direction in FIG. 6) rather than flowing from the porous layer 22 in the film thickness direction (z direction in FIG. 6) through the anode separator hole 34b. ) And is less likely to be collected at the exit via the communication path 48a. Along with this, it becomes difficult for the reactive gas to flow into the porous layer 22 on the outlet side. From the above, the difference in gas flow rate between the vicinity of the center of the cell and the gas inlet side and the outlet side is reduced, and the fuel cell according to the present embodiment improves the flowability of the fuel gas in the cell plane.

  The width L1 of the anode common rail 36 is not particularly limited as long as it is larger than the width L2 of the anode separator hole 34, but L1 is preferably at least twice as large as L2. If L1 is twice or more than L2, the gas distribution in the cell plane does not change much, but if the width L1 of the anode common rail 36 is increased more than necessary, the portion of the refrigerant flow path through which the refrigerant flows becomes relatively small. Therefore, the upper limit of L1 is about 5 times that of L2.

  In the example of FIG. 3, the width L1 of the anode common rail 36 is larger than the width L2 of the anode separator hole 34, whereas the width of the cathode common rail 40 is smaller than the width of the cathode separator hole 38. The width of 40 may be larger than the width of the cathode separator hole 38. Normally, the diffusibility of hydrogen gas, which is a fuel gas, is higher than the diffusivity of oxygen, which is an oxidant gas, so that the area of the oxidant gas manifolds 50a, 50b is larger than the area of the fuel gas manifolds 46a, 46b as shown in FIG. In many cases, the oxidizing gas manifolds 50 a and 50 b are arranged near the center with respect to the power generation region 54. In such a configuration, the width L1 of the anode common rail 36 may be larger than the width L2 of the anode separator hole 34, and the width of the cathode common rail 40 may be smaller than the width of the cathode separator hole 38. That is, the width of the cathode common rail 40 relative to the width of the cathode separator hole 38 may be determined according to the area of the fuel gas manifolds 46a and 46b and the oxidizing gas manifolds 50a and 50b, the installation position with respect to the power generation region 54, and the like. Therefore, the arrangement positions of the fuel gas manifolds 46a and 46b, the oxidizing gas manifolds 50a and 50b, and the refrigerant manifolds 52a and 52b in the non-power generation region 56 are not limited to the positions shown in FIG.

The electrolyte membrane 10 is not particularly limited as long as it has a high ion conductivity such as proton (H ⁺ ), and for example, a perfluorosulfonic acid-based solid polymer electrolyte is used. Specifically, Goreselect (registered trademark) of Japan Gore-Tex Corporation, Nafion (registered trademark) of Du Pont (Du Pont), Aciplex (registered trademark) of Asahi Kasei Co., Ltd. Perfluorosulfonic acid solid polymer electrolytes such as Flemion (registered trademark) of Asahi Glass Co., Ltd. can be used.

  The catalyst layer (the fuel electrode 12 and the air electrode 14) is made of, for example, a catalyst such as carbon carrying platinum (Pt) or the like, carbon carrying platinum (Pt) or the like together with another metal such as ruthenium (Ru), Nafion ( The film is dispersed in a resin such as a solid polymer electrolyte such as a registered trademark.

  The diffusion layers 16 and 18 are not particularly limited as long as they are materials having high conductivity and high diffusion properties of raw materials such as fuel and air, but porous conductor materials are preferable. Examples of the highly conductive material include a metal plate, a metal film, a conductive polymer, a carbon material, and the like, and carbon materials such as carbon cloth, carbon paper, and glassy carbon are preferable, and carbon cloth, carbon paper, and the like. The porous carbon material is more preferable.

  The porous layers 22 and 24 can be formed of, for example, a metal such as stainless steel or titanium, a carbon-based material, or the like. Moreover, the corrosion resistance of the porous layers 22 and 24 can be improved by attaching a carbon-based material such as graphite, carbon black, and a composite of rubber or resin using a metal such as stainless steel or titanium. . Moreover, the resistance in a cell can be reduced by comprising the porous body layers 22 and 24 with a material with high electroconductivity.

  The materials constituting the anode side separator 26, the cathode side separator 28, the anode side LLC separator 30, and the cathode side LLC separator 32 are, for example, stainless steel, aluminum or an alloy thereof, titanium or an alloy thereof, magnesium or an alloy thereof, copper, and the like. Alternatively, an alloy thereof, nickel or an alloy thereof, a metal such as steel, or a carbon-based material such as calcined carbon.

  In the fuel cell according to the present embodiment, the reaction gas can be diffused substantially uniformly in each cell surface via the porous layers 22 and 24 with the above configuration. Further, unlike the prior art, there is no need to provide a groove-type reaction gas supply channel formed in the separator, so that the contact resistance of the stack can be reduced.

  The porous layers 22 and 24 can be configured to have a lower density than the diffusion layers 16 and 18. With this configuration, the reaction gas can be diffused more uniformly in the in-plane direction of each cell.

In each unit cell 3 of the fuel cell 10, for example, when the fuel gas supplied to the fuel electrode 12 is operated as hydrogen gas and the oxidizing gas supplied to the air electrode 14 is operated as air,
2H ₂ → 4H ⁺ + 4e ⁻
Through the reaction formula (hydrogen oxidation reaction) shown in FIG. ₂ , hydrogen ions (H ⁺ ) and electrons (e ⁻ ) are generated from hydrogen gas (H ₂ ). The electrons (e ⁻ ) pass through the external circuit from the diffusion layer 16 and reach the air electrode 14 from the diffusion layer 18. In the air electrode 14, oxygen (O ₂ ) in the supplied air, hydrogen ions (H ⁺ ) that have passed through the electrolyte membrane 10, and electrons (e ⁻ ) that have reached the air electrode 14 through an external circuit,
4H ⁺ + O ₂ + 4e ⁻ → 2H ₂ O
Water is produced through the reaction formula (oxygen reduction reaction) shown in FIG. In this way, a chemical reaction occurs in the fuel electrode 12 and the air electrode 14, and charges are generated to function as a battery. And since the component discharged | emitted in a series of reaction is water, a clean battery is comprised.

  The fuel cell according to the present embodiment can be used as, for example, a small power source for mobile devices such as a mobile phone and a portable personal computer, an automobile power source, a household power source, and the like.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

<Example 1>
When the width L1 of the anode common rail 36 is larger than the width L2 of the anode separator hole 34 (L1 = L2 × 2), CFD (Computational Fluid Dynamics) analysis of the flow distribution in the cell in-plane direction was performed. The results are shown in FIG. In FIG. 7, the horizontal axis indicates the cross-sectional number obtained by dividing the power generation region into 100 at the center of the cell as shown in FIG. 8, and the vertical axis indicates the stoichiometry. The minimum flow rate (= minimum stoichiometric (flow rate) / average stoichiometric (flow rate)) of Example 1 was 87.9%. FIG. 9 shows the streamline distribution of gas in the cell plane.

<Comparative Example 1>
When the width L1 of the anode common rail 36 is smaller than the width L2 of the anode separator hole 34 (L2 = L1 × 2, L2 is the same value as in the first embodiment), the same as in the first embodiment, CFD analysis of flowability was performed. The results are shown in FIG. The minimum flow rate (= minimum stoichiometric (flow rate) / average stoichiometric (flow rate)) of Comparative Example 1 was 72.8%, which was lower than Example 1. Moreover, the streamline distribution of the gas in a cell surface is shown in FIG.

  As can be seen from FIGS. 7, 9, and 10, in the case of Example 1 (L1> L2), the in-plane uniformity of the gas flow rate is improved as compared with the case of Comparative Example 1 (L1 <L2). .

It is a schematic side view which shows an example of the fuel cell which concerns on embodiment of this invention. The schematic top view of an example of the single cell in the fuel cell which concerns on embodiment of this invention is shown. It is the schematic which shows the A-A 'cross section and B-B' cross section in FIG. FIG. 3 is an enlarged schematic diagram within a dotted line Q in FIG. 2. The expansion perspective view in the dotted line Q in FIG. 2 is shown. The expansion perspective view in the dotted line R in FIG. 2 is shown. It is a graph which shows the result of having performed CFD analysis in Example 1 and comparative example 1 of the present invention. It is a figure which shows the division | segmentation method of an electric power generation area | region in the CFD analysis of Example 1 and Comparative Example 1 of this invention. In the CFD analysis of Example 1 of this invention, it is a figure which shows the streamline distribution of the gas in a cell surface. In the CFD analysis of the comparative example 1 of this invention, it is a figure which shows the streamline distribution of the gas in a cell surface. The schematic top view of an example of the single cell in the conventional fuel cell is shown. It is the schematic which shows the CC cross section and D-D 'cross section in FIG.

Explanation of symbols

  1 Fuel cell, 3,5 single cell, 10,100 electrolyte membrane, 12,102 Fuel electrode (anode catalyst layer), 14,104 Air electrode (cathode catalyst layer), 16, 18, 106, 108 Diffusion layer, 20, 110 MEA, 22, 24, 112, 114 Porous layer, 26, 116 Anode-side separator, 28, 118 Cathode-side separator, 30, 120 Anode-side LLC separator, 32, 122 Cathode-side LLC separator, 34, 34a, 34b, 124 anode separator hole, 36, 36a, 36b, 126 anode common rail, 38, 128 cathode separator hole, 40, 130 cathode common rail, 42, 44 separator, 46a, 46b, 132 fuel gas manifold, 48a, 48b, 134 communication path, 50a, 50b Oxidizing gas manifold, 52a, 52b Refrigerant manifold, 54 Power generation region, 56 Non-power generation region, 58 Cell stack, 60 Terminal, 62 Insulator, 64 End plate, 66 Fastening member, 68 Bolt / nut, 70 Fuel cell stack.

Claims (2)

A membrane electrode assembly having an electrolyte membrane, a catalyst layer formed on both surfaces of the electrolyte membrane, and a diffusion layer formed on the surface of the catalyst layer;
A porous body layer formed on the surface of the membrane electrode assembly;
A first separator having a separator hole for sandwiching the porous body layer and supplying and discharging a reaction gas in the width direction of the porous body layer;
A second separator that sandwiches the first separator and has a common rail provided to face the separator hole;
Have
The fuel cell according to claim 1, wherein a width of the common rail is larger than a width of the separator hole on at least one side of the catalyst layer. The fuel cell according to claim 1,
The fuel cell according to claim 1, wherein a width of the common rail is larger than a width of the separator hole on an anode side of the catalyst layer.

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