JP2007273326A - Fuel cell - Google Patents

Abstract

[PROBLEMS] To prevent flooding due to generated water generated during power generation and smoothly supply gas.
For example, on the cathode side of a fuel cell, generated water 50 generated during power generation is preferentially applied to a cathode gas diffusion layer 14b of a membrane-electrode assembly 16 and a region facing a rib 22b of a cathode side separator 22. A drainage channel region 30 is formed for passing through and draining to the oxidant gas channel 22a. Thereby, the generated water 50 passes through the drainage channel region 30 preferentially and is drained. Further, the oxidant gas from the oxidant gas flow path 22a preferentially passes through the gas passage region 40 and is supplied toward the cathode catalyst layer 14a.
[Selection] Figure 2

Description

  The present invention relates to a fuel battery cell, and more particularly to prevention of flooding of generated water during power generation in the fuel battery cell.

  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 A fuel cell that generates electric power by converting chemical energy into electric energy has attracted attention.

  In general, a solid polymer electrolyte fuel cell is configured by stacking a plurality of fuel cells each having a membrane-electrode assembly (MEA) sandwiched between separators. A membrane-electrode assembly in a fuel cell has a structure in which a hydrogen electrode (anode electrode) and an air electrode (cathode electrode) are respectively provided on both sides of a polymer electrolyte membrane made of a polymer ion exchange membrane. Each of the hydrogen electrode (anode electrode) and the air electrode (cathode electrode) includes a catalyst layer formed on the polymer electrolyte membrane and a gas diffusion layer formed thereon. That is, the membrane-electrode assembly has a structure in which the polymer electrolyte membrane is sandwiched between the catalyst layers and further sandwiched between the gas diffusion layers.

  During power generation of a polymer electrolyte fuel cell, hydrogen gas is supplied as a fuel gas (anode gas) on the hydrogen electrode side of each fuel cell, and a reaction to convert hydrogen ions into electrons is performed. The inside moves to the air electrode side, and the electrons reach the air electrode through an external circuit. On the other hand, on the air electrode side in each fuel cell, oxygen gas or air is supplied as an oxidant gas (cathode gas), and hydrogen ions, electrons, and oxygen react to generate water.

  By the way, in the polymer electrolyte fuel cell, in order to maintain ionic conductivity, it is necessary to appropriately humidify the electrolyte membrane. In general, the fuel gas and the oxidant gas are previously humidified in the fuel cell. To be supplied. That is, water needs to be present in the electrolyte membrane in each fuel cell for humidification.

  Therefore, as a structure of a fuel cell that can generate power stably and with excellent characteristics by making the wettability of the solid polymer membrane and the electrode catalyst layer uniform, for example, a technique described in Patent Document 1 has been proposed. In this technique, in the gas diffusion layer sandwiched between the cathode catalyst layer and the cathode separator plate, the region facing the oxidant gas flow path is the region facing the rib within a certain range from the oxidant gas inlet side. It is adjusted so that water retention is higher than that. As a result, the tendency that the solid polymer membrane and the electrode catalyst layer are more likely to dry in the region facing the oxidant gas flow path than the region facing the rib is suppressed, and these are more uniformly moisturized. .

JP 2002-124270 A

  By the way, when water is generated in the fuel cell (catalyst layer) with power generation as described above, a part of the generated water is condensed in the gas diffusion layer of the membrane-electrode assembly. At this time, if water condenses and stays in the gas diffusion layer, the staying water hinders the supply of the oxidant gas (cathode gas) on the air electrode side. As a result, flooding occurs and power generation performance is reduced. Therefore, it is preferable that the generated water is discharged from the fuel cell (air electrode side) as much as possible so as not to stay in the gas diffusion layer.

  However, in the conventional technology as described above, the region facing the oxidant gas flow path is a region having high water retention in the gas diffusion layer, so in this region (in the gas diffusion layer) or in this region There may occur a situation in which water stays at the interface between the gas diffusion layer and the catalyst layer and causes flooding. In particular, under a high load condition of a fuel cell in which a large amount of water is generated during power generation, a situation in which power generation performance is degraded due to flooding is likely to occur.

  An object of the present invention is to provide a fuel cell that prevents flooding during power generation and enables smooth gas supply.

  The present invention provides a membrane-electrode assembly having an electrolyte membrane, and a pair of electrodes comprising a catalyst layer and a gas diffusion layer sandwiching the electrolyte membrane, and a surface facing the gas diffusion layer of the membrane-electrode assembly. And a pair of separators having a rib formed between the gas passages, and the membrane-electrode assembly is sandwiched between the pair of separators. In the gas diffusion layer, a drainage channel region for preferentially passing the generated water generated during power generation and draining the gas channel is formed in a region facing the rib in the gas diffusion layer. Is.

  Here, it is preferable that the drainage channel region is wider than the rib, and at least one end side of the drainage channel region is in contact with the gas channel.

  Moreover, it is preferable that the said drainage channel area | region has a large pore diameter compared with the other area | region in the said gas diffusion layer.

  Moreover, it is preferable that a region having a pore diameter smaller than that of the drainage channel region is formed in a region on the catalyst layer side of the drainage channel region in the gas diffusion layer.

  Moreover, it is preferable that the said drainage channel area | region is highly hydrophilic compared with the other area | region in the said gas diffusion layer.

  Moreover, it is preferable that a region having a lower hydrophilicity than the drainage channel region is formed in a region on the catalyst layer side of the drainage channel region in the gas diffusion layer.

  Moreover, it is preferable that regions other than the drainage channel region in the gas diffusion layer have water repellency.

  The separator preferably has a higher hydrophilicity than the drainage channel region.

  According to the present invention, flooding due to generated water generated during power generation can be prevented, and oxidant gas can be supplied smoothly.

  Embodiments of the present invention will be described below.

  FIG. 1 shows an example of the configuration of a fuel cell in an embodiment of the present invention. As shown in FIG. 1, the fuel cell 1 includes a membrane-electrode assembly 16 (MEA: Membrane-Electrode Assembly) having an electrolyte membrane 10, a hydrogen electrode (anode electrode) 12, and an air electrode (cathode electrode) 14; An anode side separator 20 and a cathode side separator 22 are included.

  The hydrogen electrode (anode electrode) 12 includes an anode catalyst layer 12a and an anode gas diffusion layer 12b. The air electrode (cathode electrode) 14 includes a cathode catalyst layer 14a and a cathode gas diffusion layer 14b.

  The anode-side separator 20 has a plurality of fuel gas passages 20a through which fuel gas (anode gas) flows and ribs formed between the fuel gas passages 20a on the surface facing the anode gas diffusion layer 12b. 20b. Similarly, the cathode-side separator 22 has a plurality of oxidant gas passages 22a through which an oxidant gas (cathode gas) flows on the surface facing the cathode gas diffusion layer 14b, and between the oxidant gas passages 22a. And a rib 22b formed on the surface. The separators 20 and 22 sandwich the membrane-electrode assembly 16 with the ribs 20b and 22b of the separators 20 and 22 in contact with the gas diffusion layers 12b and 14b.

  Here, in the gas diffusion layers 12b and 14b of the fuel cell 1 in the present embodiment, the generated water generated during the power generation is supplied to the gas flow path in the region facing the ribs 20b and 22b in the gas diffusion layers 12b and 14b. An area (drainage area) 30 for draining is formed, while the gas flow paths 20a, 22a to the catalyst layers 12a, 14a are formed in areas facing the gas flow paths 20a, 22a in the gas diffusion layers 12b, 14b. A region (gas passage region) 40 for supplying (passing) gas toward the surface is formed.

  FIG. 2 shows an example of the configuration of the gas diffusion layer of the fuel cell in the embodiment of the present invention. FIG. 2 shows the configuration of the cathode gas diffusion layer 14b.

  As shown in FIG. 2, on the oxidant gas flow path side in the cathode gas diffusion layer 14b, in a region facing the rib 22b (rib opposed region), a region facing the oxidant gas flow channel 22a (gas flow channel facing region). ), The pore diameter is larger. Thereby, compared with a gas flow path opposing area | region, the produced | generated water 50 becomes easy to pass in a rib opposing area | region. That is, the produced water 50 passes through the rib facing region with priority. At this time, since the pore diameter is small in the gas flow channel facing region, the generated water 50 is difficult to pass through, but the oxidant gas easily passes from the oxidant gas flow channel 22a toward the cathode catalyst layer 14a. Can do. Therefore, a small pore diameter in the gas channel facing region does not hinder the supply of the oxidant gas. Since the generated water 50 preferentially passes through the rib facing area, the generated water 50 is less likely to stay in the gas flow path facing area. Therefore, in the gas flow path facing area, the oxidant gas flow path 22a It becomes possible to pass the oxidant gas preferentially toward the cathode catalyst layer 14a.

  The pore diameter can be adjusted by, for example, applying a paste-like coating agent (for example, a paste-like water-repellent coating agent) to the gas channel facing region to reduce the pore size in the gas channel facing region. good. Accordingly, the pore diameter can be adjusted so that the pore diameter is larger in the rib facing area than in the gas flow path facing area.

  As described above, in order to drain the generated water 50 from the cathode catalyst layer 14a to the oxidant gas flow path 22a, the area 30 (drainage area) is preferentially passed, and the oxidant gas is passed from the oxidant gas flow path 22a. A region (gas passage region) 40 that is preferentially passed to be supplied to the cathode catalyst layer 14a is formed in the cathode gas diffusion layer 14b so as to prevent flooding during power generation, and an oxidant. Gas can be supplied smoothly. Such a structure is particularly effective when a large amount of water is generated under high load conditions.

  Further, in the cathode gas diffusion layer 14b in the present embodiment, the width of the drainage channel region 30 formed as described above is set wider than the width of the rib 22b, and both end portions of the drainage channel region 30 are oxidizers. It arrange | positions so that the gas flow path 22a may be contact | connected. On the other hand, the width of the gas passage region 40 is set to be narrower than the width of the oxidant gas flow path 22a. By setting the widths of the drainage channel region 30 and the gas passage region 40 as described above, the generated water that has passed through the drainage channel region 30 is ribbed from both ends of the drainage channel region 30 into the oxidant gas channel 22a. It becomes possible to drain smoothly along the wall surface 22b (the inner wall of the oxidant gas flow path 22a). In addition, although the both ends of the drainage channel area | region 30 are arrange | positioned so that the oxidant gas flow path 22a may be contacted in the figure, you may arrange | position so that only the part of one end side may contact | connect the oxidant gas flow path 22a.

  Further, in the present embodiment, as shown in the figure, an area having a small pore diameter on the entire surface on the cathode catalyst layer 14a side in the cathode gas diffusion layer 14b (an area having approximately the same size as the gas flow channel facing area). ) Is formed. That is, a region where the generated water 50 is difficult to pass is formed on the cathode catalyst layer 14 a side of the drainage channel region 30, similar to the gas passage region 40.

  With this configuration, the generated water 50 generated in the cathode catalyst layer 14a is more easily moved toward the electrolyte membrane 10 than in the cathode gas diffusion layer 14b, so that the humidified state of the electrolyte membrane 10 is changed. The generated water 50 can be used for holding.

  Further, the moisture contained in the electrolyte membrane 10 can be prevented from being drained to the oxidant gas flow path 22a via the cathode catalyst layer 14a and the cathode gas diffusion layer 14b, so that the humidified state of the electrolyte membrane 10 can be maintained. It becomes.

  In the configuration shown in FIG. 2 as well, a part of the generated water 50 passes through the cathode gas diffusion layer 14b across the small area of the pore diameter formed on the cathode catalyst layer 14a side. It moves into the layer 14b. In particular, when a large amount of water is generated under high load conditions, a large amount of generated water 50 flows into the cathode gas diffusion layer 14b. At this time, the generated water 50 that has flowed into the cathode gas diffusion layer 14b passes through the drainage channel region 30 and smoothly enters the oxidant gas channel 22a from both ends of the drainage channel region 30 along the wall surface of the rib 22b. To be drained. On the other hand, the oxidant gas passes through the gas passage region 40 and is supplied from the oxidant gas flow path 22a toward the cathode catalyst layer 14a.

  As described above, by forming the drainage channel region 30 and the gas passage region 40 separately in the cathode gas diffusion layer 14b, the oxidant gas can be supplied smoothly while preventing flooding during power generation. be able to. Such a structure is particularly effective when a large amount of water is produced under high load conditions.

  Further, a region similar to the gas passage region 40 through which the generated water 50 is difficult to pass is formed on the entire surface of the cathode gas diffusion layer 14b on the cathode catalyst layer 14a side, thereby generating the cathode catalyst layer 14a. The generated water 50 moves more easily toward the electrolyte membrane 10 than the cathode gas diffusion layer 14b, and the humidified state of the electrolyte membrane 10 can be maintained using the generated water 50. Further, the moisture contained in the electrolyte membrane 10 can be prevented from being drained to the oxidant gas flow path 22a via the cathode catalyst layer 14a and the cathode gas diffusion layer 14b, so that the humidified state of the electrolyte membrane 10 can be maintained. It becomes.

  In addition, as a method of forming the drainage channel region 30 and the gas passage region 40 separately, a method other than changing the pore diameter as in the above-described embodiment may be used.

  For example, the gas passage region 40 formed in the gas flow channel facing region is a region having high water repellency (low hydrophilicity) by performing water repellent treatment such as water repellent coating. On the other hand, the drainage channel region 30 formed in the rib-facing region has lower water repellency (hydrophilicity) than the gas passage region 40 without performing water repellency treatment or by performing treatment for increasing hydrophilicity. High) area.

  According to the above structure, the generated water 50 is unlikely to be present in the gas passage region 40, and therefore preferentially passes through the drainage channel region 30. Further, since the generated water 50 is unlikely to exist in the gas passage region 40, the oxidant gas easily passes from the oxidant gas flow path 22a to the cathode catalyst layer 14a. Accordingly, even with such a structure utilizing water repellency, the oxidant gas can be supplied smoothly while preventing flooding during power generation, as in the above embodiment.

  At this time, the region on the cathode catalyst layer 14a side in the cathode gas diffusion layer 14b is subjected to a water repellency treatment entirely along the cathode catalyst layer 14a to be a region having high water repellency (low hydrophilicity). Thereby, the generated water 50 generated in the cathode catalyst layer 14a is more easily moved toward the electrolyte membrane 10 than in the cathode gas diffusion layer 14b. Therefore, the generated water 50 is maintained in order to maintain the humidified state of the electrolyte membrane 10. 50 can be used. Further, since moisture contained in the electrolyte membrane 10 can be prevented from draining into the oxidant gas flow path 22a through the cathode catalyst layer 14a and the cathode gas diffusion layer 14b, the humidified state of the electrolyte membrane 10 can be maintained. It becomes.

  Further, it is preferable to use the cathode separator 22 made of a hydrophilic material higher than the hydrophilicity in the drainage channel region 30. According to this, the generated water 50 easily moves from the drainage channel region 30 toward the cathode side separator 22 by utilizing the level of hydrophilicity, and as a result, the oxidant gas of the cathode side separator 22 from the drainage channel region 30. Drainage into the flow path 22a becomes even smoother.

  In the above-described embodiment, the configuration of the cathode gas diffusion layer 14b has been described. Of course, the same configuration may be applied to the anode gas diffusion layer 12b.

It is the schematic which shows an example of a structure of the fuel cell concerning embodiment of this invention. It is the schematic which shows an example of a structure of the gas diffusion layer of the fuel battery cell which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell, 10 Electrolyte membrane, 12 Hydrogen electrode (anode electrode), 12a Anode catalyst layer, 12b Anode gas diffusion layer, 14 Air electrode (cathode electrode), 14a Cathode catalyst layer, 14b Cathode gas diffusion layer, 16 Membrane- Electrode assembly, 20 anode side separator, 20a fuel gas flow path, 20b rib, 22 cathode side separator, 22a oxidant gas flow path, 22b rib, 30 drainage channel area, 40 gas passage area, 50 product water.

Claims (8)

A membrane-electrode assembly having an electrolyte membrane and a pair of electrodes comprising a catalyst layer and a gas diffusion layer sandwiching the electrolyte membrane;
A pair of separators having a plurality of gas passages through which a gas flows and ribs formed between the gas passages on a surface facing the gas diffusion layer of the membrane-electrode assembly;
And the membrane-electrode assembly is sandwiched between the pair of separators,
In the region facing the rib in the gas diffusion layer, a drainage channel region for preferentially passing the generated water generated during power generation and draining it to the gas channel was formed.
The fuel cell characterized by the above-mentioned. The fuel cell according to claim 1,
The drainage channel region is wider than the rib, and at least one end side of the drainage channel region is in contact with the gas channel,
Fuel cell The fuel cell according to claim 1 or 2,
The fuel cell according to claim 1, wherein the drainage channel region has a larger pore diameter than other regions in the gas diffusion layer. The fuel cell according to claim 3,
In the region of the gas diffusion layer on the catalyst layer side of the drainage channel region, a region having a pore diameter smaller than the drainage channel region was formed.
The fuel cell characterized by the above-mentioned. A fuel cell according to any one of claims 1 to 4,
The fuel cell according to claim 1, wherein the drainage channel region has higher hydrophilicity than other regions in the gas diffusion layer. A fuel cell according to any one of claims 1 to 5,
In the region on the catalyst layer side of the drainage channel region in the gas diffusion layer, a region having a lower hydrophilicity than the drainage channel region was formed,
The fuel cell characterized by the above-mentioned. The fuel cell according to any one of claims 1 to 6,
A region other than the drainage channel region in the gas diffusion layer has water repellency,
The fuel cell characterized by the above-mentioned. The fuel cell according to any one of claims 1 to 7,
The separator has a higher hydrophilicity than the drainage channel region;
The fuel cell characterized by the above-mentioned.

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