JP4872252B2 - Fuel cell - Google Patents

Description

  The present invention relates to a fuel cell, and more particularly to a technique for suppressing a decrease in power generation performance of a fuel cell.

  A fuel cell that generates electricity using an electrochemical reaction between hydrogen and oxygen has attracted attention. A fuel cell generally has a configuration in which power generators and separators are alternately stacked. For example, the power generation body includes an MEA (also referred to as a membrane electrode assembly) in which a cathode electrode layer is disposed on one surface of an electrolyte layer and an anode electrode layer is disposed on the other surface. And a porous body layer disposed on both sides. In general, a cathode electrode layer and an anode electrode layer (hereinafter collectively referred to as an “electrode layer”) and a porous layer are used to diffuse reaction gas (air containing oxygen and fuel gas containing hydrogen) inside. It is composed of a porous body having a large internal porosity. In the present specification, the electrode layer and the porous body layer are collectively referred to as a “diffusion layer”.

  A reactive gas is supplied to the diffusion layer via a separator. The reaction gas supplied to the diffusion layer is diffused inside the diffusion layer and used for the electrochemical reaction.

  Water that has been generated and condensed due to an electrochemical reaction in the fuel cell (hereinafter referred to as “condensed water”) may flow into the diffusion layer. Condensed water inside the diffusion layer is transported to the downstream side by the flow of the reaction gas, and is discharged to the outside of the diffusion layer. However, if the condensed water is not discharged and stays inside the diffusion layer, the flow of the reaction gas inside the diffusion layer is hindered, and the power generation performance of the fuel cell may be reduced. Since the condensed water is carried by the flow of the reaction gas, the flow of the reaction gas is likely to be hindered due to the retention of the condensed water, particularly in the portion of the diffusion layer on the downstream side of the reaction gas.

  In order to suppress such a flow inhibition of the reaction gas, a technique is disclosed in which the number of pores inside the diffusion layer is increased from the upstream portion to the downstream portion of the reaction gas (for example, Patent Document 1).

JP-A-8-124583

  However, in the above prior art, since the number of pores in the downstream portion is large in the diffusion layer, the flow resistance of the reactive gas in the downstream portion is reduced, and the flow velocity of the reactive gas is reduced. Therefore, the condensed water is not easily discharged to the outside of the diffusion layer due to the flow of the reaction gas, and is likely to stay inside the diffusion layer. As a result, in the conventional technology, the flow of the reaction gas in the diffusion layer is likely to be hindered, and the power generation performance of the fuel cell may be reduced.

  The present invention has been made to solve the above-described conventional problems, and an object of the present invention is to provide a technique that can suppress a decrease in power generation performance of a fuel cell.

In order to solve at least a part of the above problems, a fuel cell of the present invention includes:
An electrolyte layer;
A diffusion layer disposed on both sides of the electrolyte layer, and supplying a reaction gas to the electrolyte layer by circulating a reaction gas inside;
A separator disposed on both sides of the diffusion layer and supplying a reaction gas to the diffusion layer,
The separator has a flat surface facing the diffusion layer,
The diffusion layer includes at least one layer;
At least one of the diffusion layers is configured such that the closer the upstream side of the flow of the reactive gas, the smaller the flow resistance of the reactive gas inside.

  This fuel cell is configured such that at least one of the diffusion layers is closer to the upstream side of the flow of the reaction gas, so that the flow resistance of the reaction gas in the interior becomes smaller. The portion closer to the upstream side is smaller and the portion closer to the downstream side is larger. Therefore, discharge of condensed water by the flow of the reaction gas is promoted in a portion near the downstream side where condensate water is likely to stay. Therefore, this fuel cell can suppress a decrease in power generation performance.

  In the fuel cell, at least one of the diffusion layers may have a higher porosity in a portion closer to the upstream side of the flow of the reaction gas.

  In this way, at least one layer of the diffusion layer can be configured such that the flow resistance of the reaction gas inside becomes smaller as the portion is closer to the upstream side of the flow of the reaction gas.

  Further, in the fuel cell, the separator has a supply port for supplying a reaction gas to the diffusion layer on a surface facing the diffusion layer, and a discharge port for discharging the reaction gas from the diffusion layer. The flow direction of the reactive gas in at least one of the diffusion layers may be a direction from a portion close to the supply port to a portion close to the discharge port.

  In the fuel cell, the diffusion layer includes a gas diffusion layer and a porous layer, the porous layer is in contact with the separator surface, and at least one of the diffusion layers is the porous layer. It may be a body layer.

  In addition, this invention can be implement | achieved in various aspects, for example, can be implement | achieved in aspects, such as a fuel cell, a fuel cell system, a fuel cell vehicle, those manufacturing methods.

Next, embodiments of the present invention will be described in the following order based on examples.
A. Example:
B. Variations:

A. Example:
1 and 2 are explanatory views schematically showing a cross-sectional configuration of a fuel cell 100 as an embodiment of the present invention. FIG. 3 is an explanatory diagram schematically showing a planar configuration of a separator 300 used in the fuel cell 100 as an embodiment of the present invention. FIG. 4 is an explanatory diagram schematically showing a planar configuration of the power generator 200 and the seat portion 400 used in the fuel cell 100 as an embodiment of the present invention. FIG. 1A shows a cross-sectional configuration of the fuel cell 100 taken along the section 1-1 in FIGS. 3 and 4, and FIG. 2A shows a section 2-2 in FIGS. 2 shows a cross-sectional configuration of the fuel cell 100 taken along the line. 1B is an enlarged view of the X1 portion in FIG. 1A, and FIG. 2B is an enlarged view of the X2 portion in FIG. 2A. FIG. 3 shows a plane of the separator 300 as viewed from the lower side in FIGS. 1 and 2. FIG. 4 illustrates a plan view of the power generation body 200 and the seat portion 400 as viewed from the lower side in FIGS. 1 and 2. In FIG. 3, a region PA surrounded by a two-dot chain line represents a region in contact with the power generation body 200 (see FIGS. 1 and 2).

  As shown in FIGS. 1 and 2, the fuel cell 100 of the present embodiment has a configuration in which power generators 200 and separators 300 are alternately stacked. In FIG. 1 and FIG. 2, a part (single cell) of the power generator 200 and the separator 300 included in the fuel cell 100 is extracted and shown, and the other power generator 200 and the separator 300 are not shown. . In addition, the fuel cell 100 of a present Example is a solid polymer type fuel cell.

  As shown in FIGS. 1 (a) and 2 (a), the power generation body 200 is arranged so as to sandwich the MEA (Membrane Electrode Assembly, also referred to as “membrane / electrode assembly”) 210 and the MEA 210 from both sides. An anode side porous body layer 220 and a cathode side porous body layer 230. Further, as shown in FIGS. 1B and 2B, the MEA 210 includes an electrolyte layer 212 constituted by an ion exchange membrane, and an anode side gas diffusion electrode layer disposed so as to sandwich the electrolyte layer 212 from both sides. 214 and the cathode side gas diffusion electrode layer 216. In the present specification, the anode side porous body layer 220 and the cathode side porous body layer 230 are collectively referred to simply as a “porous body layer”. The anode-side gas diffusion electrode layer 214 and the cathode-side gas diffusion electrode layer 216 are collectively referred to simply as “electrode layers”. In the present specification, the porous body layer and the electrode layer are collectively referred to as a “diffusion layer”.

  The porous body layer (the anode side porous body layer 220 and the cathode side porous body layer 230) and the electrode layer (the anode side gas diffusion electrode layer 214 and the cathode side gas diffusion electrode layer 216) have a high internal porosity and the gas is in the interior. It is comprised using the metal porous body and carbon porous body with a small pressure loss at the time of distribute | circulating. The detailed structure of the porous body layer will be described later.

  As shown in FIG. 1B and FIG. 2B, the separator 300 includes a cathode facing plate 310 facing the cathode side porous layer 230, an anode facing plate 330 facing the anode side porous layer 220, It has a three-layer structure in which an intermediate plate 320 sandwiched between a cathode facing plate 310 and an anode facing plate 330 is laminated. The three plates (cathode facing plate 310, anode facing plate 330, and intermediate plate 320) constituting the separator 300 are metal thin plates having a substantially rectangular plane.

  As shown in FIGS. 1 and 3, the separator 300 has a flow path through which air as an oxidizing gas flows. That is, the separator 300 includes a through-hole 342 that forms an air supply path 610 (FIG. 1A), a through-hole 352 that forms an air discharge path 620 (FIG. 1A), and air to the air supply path 610. In order to communicate the air flow path 344 for guiding air from the inside to the inside, the air flow path 354 for guiding air to the air discharge path 620, the air flow paths 344 and 354, and the cathode-side porous body layer 230, respectively. It has an air supply port 346 and an air discharge port 356 formed in the cathode facing plate 310. As indicated by arrows in FIG. 1, the air supplied to the air supply path 610 flows into the cathode side porous body layer 230 through the through-hole 342, the air flow path 344, and the air supply port 346. Thereafter, the air is used for the electrochemical reaction while passing through the inside of the cathode-side porous layer 230, and the unused air passes through the air discharge port 356, the air flow path 354, and the through-hole 352 to the air discharge path 620. Discharged.

 Similarly, as shown in FIGS. 2 and 3, the separator 300 is formed with a flow path through which hydrogen-rich fuel gas flows. That is, the separator 300 includes a through port 362 that forms a fuel supply path 630 (FIG. 2A), a through port 372 that forms a fuel discharge path 640 (FIG. 2A), and a fuel gas supply path. A fuel flow path 364 that leads from 630 to the inside, a fuel flow path 374 that guides fuel gas to the fuel discharge path 640, and the fuel flow paths 364 and 374 and the anode-side porous body layer 220 communicate with each other. Therefore, a fuel supply port 366 and a fuel discharge port 376 formed in the anode facing plate 330 are provided. As indicated by arrows in FIG. 2, the fuel gas supplied to the fuel supply path 630 flows into the anode-side porous body layer 220 through the through-hole 362, the fuel flow path 364, and the fuel supply port 366. Thereafter, the fuel gas is used for the electrochemical reaction while passing through the anode side porous layer 220, and the unused fuel gas passes through the fuel discharge port 376, the fuel flow path 374, and the through-hole 372, and the fuel discharge path. It is discharged to 640.

  Further, the separator 300 is formed with a flow path through which a cooling medium for cooling the fuel cell 100 flows. That is, the separator 300 has a through hole 382 (FIG. 3) that forms a cooling medium supply path (not shown) for supplying the cooling medium, and a through hole 392 (FIG. 3) that forms a cooling medium discharge path (not shown) for discharging the cooling medium. And a cooling medium flow path 384 (FIGS. 3 and 1A) that communicates the two through holes 382 and 392. The cooling medium supplied to the cooling medium supply path is discharged to the cooling medium discharge path through the through hole 382, the cooling medium flow path 384, and the through hole 392.

  The formation of the flow path through which the air, fuel gas, and cooling medium flow in the separator 300 described above is performed on three plates (cathode facing plate 310, anode facing plate 330, and intermediate plate 320) constituting the separator 300 in a predetermined manner. This is done by punching. Therefore, in the fuel cell 100 according to the present embodiment, the manufacture of the separator 300 can be facilitated and the cost can be reduced.

  As shown in FIGS. 1 and 2, a sheet unit 400 is provided around the MEA 210. As shown in FIG. 4, the seat part 400 has a plurality of holes for forming a flow path through which the above-described air, fuel gas, and cooling medium flow. That is, the seat portion 400 includes an air supply path formation hole 442 that forms an air supply path 610 (FIG. 1A), and an air discharge path formation hole 452 that forms an air discharge path 620 (FIG. 1A). The fuel supply path forming hole 462 that forms the fuel supply path 630 (FIG. 2A), the fuel discharge path forming hole 472 that forms the fuel discharge path 640 (FIG. 2A), and the cooling medium supply path ( A cooling medium supply path forming hole 482 that forms a cooling medium discharge path (not shown), and a cooling medium discharge path forming hole 492 that forms a cooling medium discharge path (not shown).

  As shown in FIGS. 1 and 2, a seal portion 500 is provided between the sheet portion 400 and the separator 300. In this embodiment, the seal portion 500 is formed of a resin material such as silicon rubber, butyl rubber, or fluororubber. The seal unit 500 is sandwiched between the separator 300 and the sheet unit 400 and compressed, thereby being brought into close contact with the separator 300 and the sheet unit 400 and performing a seal. The seal unit 500 suppresses leakage along the layer direction of the reaction gas (air and fuel gas) supplied to the anode-side porous layer 220 and the cathode-side porous layer 230, and the above-described various flow paths (air supply). A path 610, an air discharge path 620, a fuel supply path 630, a fuel discharge path 640, a cooling medium supply path, and a cooling medium discharge path). Therefore, as shown in FIG. 4, the seal portion 500 is disposed so as to surround the anode-side porous body layer 220 of the power generator 200 and to surround each hole formed in the sheet portion 400. In FIG. 5, a contact portion (seal line) of the seal portion 500 with the separator 300 is shown as the seal portion 500. Similarly, on the cathode side, the seal portion 500 is disposed so as to surround the cathode-side porous body layer 230 of the power generator 200 and to surround each hole formed in the sheet portion 400.

  FIG. 5 is an explanatory view showing the structure of the cathode-side porous body layer 230 in this example. In FIG. 5, positions (see FIGS. 1 and 4) facing the air supply port 346 and the air discharge port 356 in the plane of the cathode side porous layer 230 are indicated by broken lines, and the air inside the cathode side porous layer 230 is also shown in FIG. The flow direction is indicated by arrows.

  As shown in FIG. 5, the cathode-side porous body layer 230 of this example includes a first porous body layer 231, a second porous body layer 232, a third porous body layer 233, and a fourth porous body layer 234. , Is composed of. Each porous body layer (the first porous body layer 231, the second porous body layer 232, the third porous body layer 233, and the fourth porous body layer 234) constituting the cathode side porous body layer 230 has an air flow direction, respectively. It is formed in a strip-like rectangular shape extending in a direction perpendicular to the vertical direction. Each porous body layer constituting the cathode-side porous body layer 230 has a first porous body layer 231, a second porous body layer 232, a third porous body layer 233, and a fourth porous body layer 234 along the air flow direction. Are arranged in the order. The air supply port 346 faces the first porous layer 231 and the air discharge port 356 faces the fourth porous layer 234.

  Each porous body layer constituting the cathode side porous body layer 230 is composed of porous bodies having different porosity. FIG. 5 conceptually shows a part of the voids 239 formed inside each porous body layer (Y1 part, Y2 part, Y3 part, Y4 part) in an enlarged manner. As shown in FIG. 5, the porosity of each porous body layer is the largest in the first porous body layer 231, and decreases in the order of the second porous body layer 232, the third porous body layer 233, and the fourth porous body layer 234. It has become. That is, the porosity is larger as the porous body layer is closer to the upstream side of the air flow. Therefore, the flow path resistance inside each porous body layer is smaller as the porous body layer is closer to the upstream side of the air flow. In FIG. 5, the voids 239 are shown as independent voids in order to conceptually indicate the porosity inside the porous body layer. However, in actuality, the voids 239 communicate with other voids 239 and air A flow path is formed.

  The cathode-side porous layer 230 in the present embodiment is configured such that the portion of the internal channel resistance that is closer to the upstream side of the air flow becomes smaller, so that the air flowing through the cathode-side porous layer 230 is reduced. The flow velocity is smaller as the portion is closer to the upstream side, and is larger as the portion is closer to the downstream side. Condensed water is likely to stay in the portion close to the downstream side of the cathode-side porous layer 230. However, in the cathode-side porous layer 230 of the present embodiment, the air flow rate in the portion close to the downstream side is large. Water discharge is promoted. As a result, it is possible to suppress air flow obstruction inside the cathode-side porous body layer 230 due to the retention of condensed water. Therefore, in the fuel cell 100 of the present embodiment, it is possible to suppress a decrease in power generation performance.

  In addition, since the fuel cell 100 of the present embodiment employs the separator 300 having a flat surface facing the porous body layer, air is supplied from the air supply port 346 (FIG. 1) of the separator 300 to the cathode side porous. After being supplied to the upstream portion (first porous body layer 231) of the body layer 230, it is supplied to the power generation while diffusing inside the cathode side porous body layer 230. Therefore, for example, compared to the case where a separator having a groove as an air flow path formed on the surface, condensate water tends to stay inside the cathode-side porous body layer 230, and condensate water stays. The impact on power generation performance is also significant. In the fuel cell 100 of the present embodiment, even when such a separator 300 having a flat surface facing the porous body layer is employed, air flow inhibition inside the cathode-side porous body layer 230 due to the retention of condensed water. Can be suppressed, and a decrease in power generation performance can be suppressed.

  Further, in the fuel cell 100 of the present embodiment, the air flow rate can be reduced in the portion of the cathode-side porous layer 230 close to the upstream side of the air flow, so that the MEA 210 (FIG. 1) is dried by the air flow. And an increase in electrical resistance due to drying of the MEA 210 can be suppressed. Therefore, in the fuel cell 100 of the present embodiment, it is possible to suppress a decrease in power generation performance of the fuel cell 100.

  Further, in the fuel cell 100 of the present embodiment, the flow path resistance inside the cathode-side porous body layer 230 is configured so as to become smaller as the portion nears the upstream side of the air flow, so the air in the portion close to the upstream side. The pressure drop is small. Therefore, the pressure of the air inside the cathode side porous body layer 230 is kept relatively high, and the saturated vapor pressure is also kept high. As a result, the water generated by the electrochemical reaction is less likely to condense, and air flow inhibition inside the cathode-side porous body layer 230 due to retention of condensed water can be suppressed. Therefore, in the fuel cell 100 of the present embodiment, it is possible to suppress a decrease in the power generation performance of the fuel cell 100.

B. 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.

B-1. Modification 1:
The configuration of the fuel cell 100 in the above embodiment is merely an example, and the configuration of the fuel cell 100 may be another configuration. For example, in the above embodiment, as shown in FIG. 5, the cathode side porous body layer 230 is divided into four porous body layers (first porous body layer 231, second porous body layer 232, third porous body layer 233, fourth The cathode-side porous layer 230 may be composed of three or less porous layers, or may be composed of five or more porous layers. Further, the cathode-side porous body layer 230 does not necessarily need to be constituted by a plurality of porous body layers. If the flow-path resistance is configured so as to be closer to the upstream side of the air flow, one cathode-side porous body layer 230 is required. You may be comprised by the porous body layer.

  In the above-described embodiment, the cathode-side porous layer 230 is configured such that the internal flow path resistance is smaller as the portion is closer to the upstream side of the air flow. The electrode layer 216 may also be configured such that the inner channel resistance becomes smaller as the portion is closer to the upstream side of the air flow. Similarly, the anode-side porous body layer 220 and the anode-side gas diffusion electrode layer 214 may be configured such that the inner channel resistance becomes smaller toward the upstream side of the fuel gas flow. .

  Moreover, in the said Example, although each porous body layer and each electrode layer are comprised by the metal porous body and the carbon porous body, each porous body layer and each electrode layer are other materials, such as a carbon cloth. You may comprise by.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows schematically the cross-sectional structure of the fuel cell as an Example of this invention. BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows schematically the cross-sectional structure of the fuel cell as an Example of this invention. BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows roughly the planar structure of the separator used for the fuel cell as an Example of this invention. BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows roughly the planar structure of the electric power generation body used for the fuel cell as an Example of this invention, and a sheet | seat part. Explanatory drawing which shows the structure of the porous body layer in a present Example.

Explanation of symbols

100 ... Fuel cell 200 ... Power generator 210 ... MEA
212 ... Electrolyte layer 214 ... Anode-side gas diffusion electrode layer 216 ... Cathode-side gas diffusion electrode layer 220 ... Anode-side porous layer 230 ... Cathode-side porous layer 231 ... First Porous layer 232 ... Second porous layer 233 ... Third porous layer 234 ... Fourth porous layer 239 ... Void 300 ... Separator 310 ... Cathode facing plate 320 .. Intermediate plate 330 ... Anode facing plate 342 ... Through hole 344 ... Air flow path 346 ... Air supply port 352 ... Through hole 354 ... Air flow path 356 ... Air discharge port 362 ... Through port 364 ... Fuel channel 366 ... Fuel supply port 372 ... Through port 374 ... Fuel channel 376 ... Fuel outlet 382 ... Through port 384 ... Coolant flow path 392 ... Through port 400 ... Sheet part 442 ... Air supply path formation hole 452 ... Air discharge path formation hole 462 ... Fuel supply path formation 472 ... Fuel discharge path forming hole 482 ... Cooling medium supply path forming hole 492 ... Cooling medium discharge path forming hole 500 ... Seal part 610 ... Air supply path 620 ... Air discharge path 630 ... fuel supply path 640 ... fuel discharge path

Claims (1)

A fuel cell,
An electrolyte layer;
A diffusion layer disposed on both sides of the electrolyte layer, and supplying a reaction gas to the electrolyte layer by circulating a reaction gas inside;
A separator disposed on both sides of the diffusion layer and supplying a reaction gas to the diffusion layer ,
The diffusion layer is composed of a gas diffusion layer and a porous layer,
The porous body layer is in contact with the separator surface,
The separator surface facing the porous layer is flat shape, wherein in the vicinity of the end portion of the facing surface to the porous body layer, and a supply port for supplying a reaction gas to the porous body layer, wherein the porous An exhaust port for exhausting the reaction gas from the body layer,
The reaction gas supplied from the supply port flows into the porous body layer from the surface of the porous layer facing the separator, and the reaction gas flowing out from the surface of the porous layer facing the separator is exhausted. Discharged to the exit,
The porous layer is composed of a plurality of different porous body having porosity, as part close to the portion closer to the supply port on the upstream side in the direction towards the portion close to the outlet, porosity A fuel cell in which a large porous body is disposed and the flow resistance of a reaction gas inside is reduced.

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