JP2006107752A - Membrane electrode assembly of fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane electrode assembly of a fuel cell capable of efficiently draining water produced in power generation. <P>SOLUTION: The membrane electrode assembly of the fuel cell is formed in such a way that a cathode catalyst layer 16, a cathode primary coat 17, and a cathode diffusion layer 18 are stacked on the cathode side of an electrolyte membrane, an oxygen gas passage 24 is installed on the outside of the cathode diffusion layer 18, and each layer and the electrolyte membrane are arranged in the gravity acting direction. The membrane electrode assembly of the fuel cell contains a conductive material and a water repellent material in the primary coat 17, and the ratio of the water repellent material is gradually increased in the gravity acting direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a membrane electrode assembly for a fuel cell that generates power by supplying hydrogen gas to the anode side and oxygen gas to the cathode side.

FIG. 12 is a view for explaining a main part of a membrane electrode assembly of a conventional fuel cell.
The cathode and anode layers 102 and 103 are laminated on the front and back surfaces of the electrolyte membrane 101 constituting the membrane electrode assembly 100 of the fuel cell, the cathode diffusion layer 104 is laminated on the cathode layer 102, and the anode diffusion layer is formed on the anode layer 103. 105 are stacked, an oxygen gas flow path 106 is provided outside the cathode diffusion layer 104, and a hydrogen gas flow path (not shown) is provided outside the anode diffusion layer 105.
Oxygen gas flows from the supply side 106a of the oxygen gas flow path 106 toward the discharge side 106b.

By flowing oxygen gas through the oxygen gas channel 106 and flowing hydrogen gas through the hydrogen gas channel, hydrogen (H ₂ ) is brought into contact with the catalyst in the anode layer 103 and oxygen ( O ₂ ) is brought into contact to generate a current.

FIG. 13 is a cross-sectional view showing a main part of a membrane electrode assembly of a conventional fuel cell.
The cathode layer 102 includes a catalyst layer 102a and a base layer 102b, and the anode layer 103 includes a catalyst layer 103a and a base layer 103b.
Hydrogen ions (H ⁺ ) generated by the reaction in the anode layer 103 (see FIG. 12) permeate the electrolyte membrane 101 and flow toward the cathode layer 102 as indicated by arrows.
On the other hand, oxygen gas flows from the cathode layer 102 toward the electrolyte membrane 101 by supplying oxygen gas from the oxygen gas flow path 106 (see FIG. 12) into the cathode layer 102.

Thus, hydrogen ions (H ⁺ ) and oxygen (O ₂ ) react to generate product water (H ₂ O). The reaction between hydrogen ions (H ⁺ ) and oxygen (O ₂ ) proceeds in the catalyst layer 102a.
Part of the generated water (H ₂ O) is returned to the electrolyte membrane 101 side. This is because power generation efficiency is improved by keeping the electrolyte membrane 101 in a wet state.
A part of the remaining generated water (H ₂ O) passes through the base layer 102b and is discharged to the cathode diffusion layer 104 as indicated by the arrow A, and the other generated water (H ₂ O) passes through the cathode layer 102 by the arrow B. It descends by its own weight.
For this reason, the generated water (H ₂ O) tends to accumulate on the lower side 102c of the cathode layer 102, which hinders the increase in power generation efficiency of the membrane electrode assembly of the fuel cell.

FIG. 14 is a side view showing a main part of a membrane electrode assembly of a conventional fuel cell.
Oxygen gas flows through the oxygen gas flow path 106 from the supply side 106a toward the discharge side 106b as shown by an arrow.
On the other hand, part of the generated water (H ₂ O) flowing out from the cathode layer 102 to the cathode diffusion layer 104 evaporates and evaporates into the oxygen gas flow path, and the oxygen gas in the oxygen gas flow path 106 Carried in.

Here, oxygen gas tends to stay in the bent portions 106c and 106c of the oxygen gas channel 106, and the flow rate of oxygen gas decreases on the discharge side 106b of the oxygen gas channel 106, that is, the lower side 102c of the cathode layer 102. Tend.
For this reason, on the discharge side 106b of the oxygen gas channel 106, it is difficult to efficiently discharge the generated water evaporated in the oxygen gas channel, and the generated water easily collects on the discharge side 106b. It was an impediment to improving the power generation efficiency of the body.

In order to increase the power generation efficiency of the fuel cell membrane electrode assembly, there is provided a fuel cell membrane electrode assembly in which the distribution of the electrolyte in the catalyst layer 102a is changed so that the proportion of the electrolyte decreases as the cathode diffusion layer 104 is approached. It is known (for example, refer to Patent Document 1).
JP-A-9-180730 (FIG. 3)

According to the membrane electrode assembly of the fuel cell, the power generation efficiency can be increased by changing the distribution of the electrolyte in the catalyst layer.
However, even the membrane electrode assembly of the fuel cell disclosed in Patent Document 1 does not take measures to efficiently discharge generated water.
For this reason, there is a possibility that the generated water generated during power generation may accumulate inside the membrane electrode assembly of the fuel cell.

  An object of the present invention is to provide a membrane electrode assembly of a fuel cell that can efficiently drain generated water generated during power generation.

  According to the first aspect of the present invention, a cathode catalyst layer, a cathode base layer, and a cathode diffusion layer are laminated on the cathode side of the electrolyte membrane, and an oxygen gas flow path is provided outside the cathode diffusion layer. In the fuel cell membrane electrode assembly arranged in the direction in which the gravity acts, the cathode underlayer includes a conductive material and a water-repellent material, and the proportion of the water-repellent material gradually increases in the direction in which the gravity acts. It was made to be characterized.

  Here, in order to ensure the power generation performance of the fuel cell, the generated water generated during power generation needs to be led from the cathode catalyst layer side to the cathode diffusion layer side and drained to the outside of the cathode diffusion layer. Therefore, in order to efficiently guide the generated water from the cathode catalyst layer side to the cathode diffusion layer side, a water repellent material is included in the cathode underlayer.

By the way, when a fuel cell is used, the fuel cell is usually arranged so that the electrolyte membrane, the cathode catalyst layer, the cathode underlayer and the cathode diffusion layer are in the vertical direction, that is, in the direction in which gravity acts.
Thereby, when the generated water is guided from the cathode catalyst layer side to the cathode diffusion layer side, a part of the generated water is affected by gravity and moves in the direction in which gravity acts. Therefore, the generated water tends to accumulate on the side in the direction in which gravity acts.

Therefore, in claim 1, the ratio of the water repellent material contained in the cathode underlayer is gradually increased in the direction in which gravity acts.
Therefore, even if a part of the generated water is affected by gravity and moves in the direction in which the gravity acts, the moved generated water can be favorably guided to the cathode diffusion layer side by the water repellent material.

  Claim 2 is characterized in that the ratio of the water repellent material is increased from the cathode catalyst layer side to the cathode diffusion layer side and / or gradually increased from the supply side to the discharge side of the oxygen gas flow path. And

Here, in order to ensure the water content of the electrolyte membrane and maintain the power generation performance, it is necessary to suppress the drainage of the generated water in the vicinity of the surface of the underlayer that contacts the cathode catalyst layer.
On the other hand, on the cathode diffusion layer side, it is necessary to improve the drainage of the generated water and efficiently guide the generated water in the cathode underlayer to the cathode diffusion layer.
Therefore, in claim 2, the ratio of the water repellent material is gradually increased from the cathode catalyst layer side toward the cathode diffusion layer side.
As a result, the water content of the electrolyte membrane can be ensured, and the water produced in the cathode underlayer can be favorably guided to the cathode diffusion layer side.

Further, part of the generated water in the cathode underlayer is evaporated in the oxygen gas flow path and moves together with the oxygen gas. It is conceivable that the flow rate of this oxygen gas decreases on the discharge side of the oxygen gas flow path. For this reason, generated water tends to accumulate on the discharge side of the oxygen gas flow path.
Therefore, in claim 2, the ratio of the water repellent material is gradually increased from the supply side to the discharge side of the oxygen gas flow path.
As a result, on the discharge side of the oxygen gas flow path, the generated water of the cathode underlayer can be favorably guided to the cathode diffusion layer side.

  In the invention according to claim 1, by gradually increasing the ratio of the water repellent material contained in the cathode underlayer in the direction in which the gravity acts, the generated water that has moved in the direction in which the gravity acts can be There is an advantage that it can be well guided to the cathode diffusion layer side and the generated water generated during power generation can be drained efficiently.

  In the invention according to claim 2, the ratio of the water repellent material is increased from the cathode catalyst layer side to the cathode diffusion layer side and / or gradually increased from the supply side to the discharge side of the oxygen gas flow path. Thus, there is an advantage that the generated water of the cathode underlayer can be guided well to the cathode diffusion layer side, and the generated water can be efficiently guided from the cathode underlayer toward the cathode diffusion layer side.

The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. The drawings are viewed in the direction of the reference numerals.
FIG. 1 is a perspective view showing a fuel cell provided with a membrane electrode assembly (first embodiment) according to the present invention, in which a cell is disassembled.
The fuel cell 10 is configured by stacking a plurality of cells 11. In the cell 11, separators 13 and 14 are provided on both sides of the membrane electrode assembly 12.
The membrane electrode assembly 12 includes a cathode catalyst layer 16 laminated on the electrolyte membrane 15, a cathode underlayer 17 laminated on the catalyst layer 16, and a cathode diffusion layer 18 laminated on the underlayer 17 on the cathode side of the electrolyte membrane 15. The anode side of the electrolyte membrane 15 is formed by an anode catalyst layer 21 laminated on the electrolyte membrane 15, an anode foundation layer 22 laminated on the catalyst layer 21, and an anode diffusion layer 23 laminated on the foundation layer 22. is there.

  Further, in the cell 11, the separator 13 is provided outside the cathode diffusion layer 18 to form an oxygen gas flow path 24 (see FIG. 2) between the cathode diffusion layer 18 and the separator 13, and the separator is formed outside the anode diffusion layer 23. 14, a hydrogen gas flow path 25 (see FIG. 2) is formed by the anode diffusion layer 23 and the separator 14.

  When the fuel cell 10 is used, the electrolyte membrane 15, the cathode / anode side catalyst layers 16, 21, the cathode / anode side base layers 17, 22, and the cathode / anode side diffusion layers 18, 23 act by gravity. As an example, the fuel cell 10 is arranged so as to face the vertical direction.

Reference numerals 26 and 27 denote seals. A seal 26 is interposed between the electrolyte membrane 15 and the separator 13 to seal between the electrolyte membrane 15 and the separator 13.
A seal 27 is interposed between the electrolyte membrane 15 and the separator 14 to seal between the electrolyte membrane 15 and the separator 14.

FIG. 2 is a cross-sectional view of a membrane electrode assembly (first embodiment) of a fuel cell according to the present invention.
A cathode catalyst layer 16, a cathode base layer 17, and a cathode diffusion layer 18 are sequentially stacked on the cathode side of the electrolyte membrane 15, and an anode catalyst layer 21, an anode base layer 22, and an anode diffusion layer 23 are formed on the anode side of the electrolyte membrane 15. Laminate sequentially.

By providing the separator 13 outside the cathode diffusion layer 18, the oxygen gas flow path 24 is formed by the cathode diffusion layer 18 and the separator 13.
By providing the separator 14 outside the anode diffusion layer 23, the hydrogen gas flow path 25 is formed by the anode diffusion layer 23 and the separator 14.

FIG. 3 is an enlarged view of part 3 of FIG.
The cathode catalyst layer 16 includes, for example, large-diameter granular carbon as the conductive material 41..., And the catalyst 42 is held around the conductive material 41.

The cathode underlayer 17 includes a first layer 43 having water absorption and adhesion, and a second layer 44 having water repellency.
The first layer 43 includes, for example, small-diameter granular carbon as the conductive material 45. Since the water absorbing material functions as an adhesive, the adhesion of the cathode underlayer 17 to the cathode catalyst layer 16 can be secured.
The second layer 44 includes, for example, small-diameter granular carbon as the conductive material 41..., And includes, for example, tetrafluoroethylene as the water repellent material (fluorine resin) 46.

The conductive materials 41 and 45 affect the power generation reaction. When the conductive materials 41 and 45 increase, the power generation reaction increases, and when the conductive materials 41 and 45 decrease, the power generation reaction decreases.
The water repellent material 46 affects the drainage of the generated water. When the water repellent material 46 increases, the water repellency increases, and when the water repellent material 46 decreases, the water repellency decreases.

For example, the cathode diffusion layer 18 is obtained by subjecting a porous conductive carbon paper formed of acicular carbon fibers 47 to a water repellent treatment.
By providing the separator 13 outside the cathode diffusion layer 18, oxygen gas flow paths 24 are formed by the cathode diffusion layer 18 and the grooves 13 a of the separator 13.

By supplying the oxygen gas passage 24 oxygen (O _2), oxygen (O ₂₎ enters the cathode base layer 17 as shown by the arrow a through the cathode diffusion layer 18.
Oxygen (O ₂ ) in the cathode underlayer 17 enters the cathode catalyst layer 16 as indicated by arrow a, and oxygen (O ₂ ) in the cathode catalyst layer 16 enters the electrolyte membrane 15 as indicated by arrow a.

On the other hand, hydrogen ions (H ⁺ ) generated by the reaction in the anode catalyst layer 21 pass through the electrolyte membrane 15 and enter the cathode catalyst layer 16 side as indicated by an arrow b.
Therefore, in the cathode catalyst layer 16, hydrogen ions (H ⁺ ) and oxygen (O ₂ ) react to generate generated water.

A part of the generated water is returned to the electrolyte membrane 15 side. This is to keep the electrolyte membrane 15 in a wet state.
A part of the remaining generated water flows out from the cathode catalyst layer 16 through the cathode underlayer 17 to the cathode diffusion layer 18, and other generated water descends by its own weight in the cathode catalyst layer 16 and the cathode underlayer 17. To do.

FIG. 4 is an explanatory diagram showing component ratios constituting the cathode underlayer of the first embodiment.
A cathode base layer 17 is provided between the cathode catalyst layer 16 and the cathode diffusion layer 18, and an oxygen gas flow path 24 (see also FIG. 3) is provided along the cathode diffusion layer 18.
In order to facilitate understanding, the oxygen gas flow path 24 is described as being meandered for convenience. In the oxygen gas flow path 24, oxygen gas flows from the supply side 24a toward the discharge side 24b.

As described above, the cathode underlayer 17 (specifically, the second layer 44) includes the conductive material 41... And the water repellent material 45.
As an example of the conductive material 41..., Granular carbon corresponds. As the water repellent material 45..., A fluororesin corresponds.
Hereinafter, in the first embodiment, the second layer 44 will be described as the cathode underlayer 17 in order to facilitate understanding.

The weight ratio (hereinafter referred to as “ratio”) of the water repellent material in the cathode underlayer 17 is gradually increased from the cathode catalyst layer 16 side toward the cathode diffusion layer 18 side as shown by the first component display unit 30.
Further, as shown by the second component display unit 31, the ratio of the water repellent material is gradually increased in the direction in which gravity acts, that is, from the vertical upper side 17a to the lower side 17b of the cathode base layer 17.
Further, the ratio of the water repellent material is gradually increased from the supply side 24 a to the discharge side 24 b of the oxygen gas flow path 24 as indicated by the third component display portion 32.

On the other hand, the ratio of the conductive material in the cathode underlayer 17 is gradually decreased from the cathode catalyst layer 16 side toward the cathode diffusion layer 18 side as indicated by the fourth component display portion 33.
Further, as shown by the fifth component display unit 34, the ratio of the conductive material is gradually decreased from the upper side 17a in the vertical direction to the lower side 17b of the cathode base layer 17 in the direction in which gravity acts.
Further, the ratio of the conductive material is gradually decreased from the supply side 24a to the discharge side 24b of the oxygen gas flow path 24 as indicated by the sixth component display unit 35.

Next, an example of the ratio (wt%) of the water repellent material 46 and the conductive material 45 included in the cathode underlayer 17 will be described with reference to FIG.
In Table 1, the ratio (wt%) of the water repellent material 46 and the conductive material 45 indicates the ratio of the solid content in the cathode underlayer 17.

FIGS. 5A and 5B are explanatory views showing the ratio of the water repellent material and the conductive material included in the cathode underlayer of the first embodiment.
(A) shows the 1st, 2nd component display parts 30 and 31 of the water repellent material 46, and the 4th and 5th component display parts 33 and 34 of the electrically-conductive material 45. FIG. (B) shows the third component display part 32 of the water repellent material 46 and the sixth component display part 35 of the conductive material 45.

First, in (a), the 1st component display part 30 of the water repellent material 46 is demonstrated.
In the vicinity of the surface 37 in contact with the cathode catalyst layer 16, it is preferable that the water content on the cathode catalyst layer 16 side is secured to some extent by suppressing the drainage of generated water.
By securing the moisture content on the cathode catalyst layer 16 side to a certain extent, it is necessary to ensure the moisture content of the electrolyte membrane and to maintain good power generation.
Therefore, the ratio of the water repellent material 46 is reduced to 27 to 49 wt% in the vicinity of the surface 37 in contact with the cathode catalyst layer 16, that is, in the area 30 a of the first component display unit 30.

On the other hand, on the cathode diffusion layer 18 side, it is necessary to increase the drainage of the generated water to efficiently drain the generated water in the cathode underlayer 17.
Therefore, the ratio of the water repellent material 46 was gradually increased from the cathode catalyst layer 16 side toward the cathode diffusion layer 18 side.

Specifically, in the area 30b of the first component display unit 30, the ratio of the water repellent material 46 is 49 to 73 wt%, which is larger than the ratio of the area 30a.
Furthermore, in the area 30c of the first component display unit 30, the ratio of the water repellent material 46 is set to 73 to 85 wt%, which is larger than the ratio of the area 30b.

Next, the 4th component display part 33 of the electrically-conductive material 45 is demonstrated in (a).
In the cathode underlayer 17, it is preferable to keep the catalytic reaction high in the vicinity of the surface 37 in contact with the cathode catalyst layer 16.
Therefore, in the vicinity of the surface 37 in contact with the cathode catalyst layer 16, that is, in the area 33 a of the fourth component display portion 33, the ratio of the conductive material 45 is increased to 51 to 73 wt%.

On the other hand, it is gradually suppressed from the cathode catalyst layer 16 toward the cathode diffusion layer 18.
The ratio of the conductive material 45 was gradually decreased from the cathode catalyst layer 16 side toward the cathode diffusion layer 18 side.

Specifically, in the area 33b of the fourth component display unit 33, the ratio of the conductive material 45 is set to 27 to 51 wt%, which is smaller than the ratio of the area 33a.
Furthermore, in the area 33c of the fourth component display unit 33, the ratio of the conductive material 45 is set to 15 to 27 wt%, which is smaller than the ratio of the area 33b.

Next, in (a), the second component display part 31 of the water repellent material 46 will be described.
As shown in FIG. 1, when the fuel cell 10 is used, the electrolyte membrane 15, the cathode / anode side catalyst layers 16 and 21, the cathode / anode side base layers 17 and 22, and the cathode / anode side diffusion are usually used. As an example, the fuel cell 10 is arranged so as to face the vertical direction so that the layers 18 and 23 face the direction in which gravity acts.

Therefore, in the cathode underlayer 17, the generated water moves from the upper side 17a to the lower side 17b due to gravity (that is, its own weight), so that the generated water does not easily accumulate on the upper side 17a.
Therefore, in the area 31a of the second component display unit 31, the ratio of the water repellent material 46 is reduced to 27 to 56 wt%.

On the other hand, the generated water tends to accumulate on the lower side 17b of the cathode underlayer 17 due to its own weight. Therefore, it is necessary to increase the drainage of the generated water at the lower side 17b of the cathode underlayer 17 and drain the generated water efficiently.
Therefore, the ratio of the water repellent material 46 was gradually increased from the upper side 17a to the lower side 17b of the cathode underlayer 17.

Specifically, in the area 31b of the second component display unit 31, the ratio of the water repellent material 46 is set to 56 to 63 wt%, which is larger than the ratio of the area 31a.
Further, in the area 31c of the second component display unit 31, the ratio of the water repellent material 46 is set to 63 to 85 wt%, which is larger than the ratio of the area 31b.

Then, in (a), the 5th component display part 35 of the electrically-conductive material 45 is demonstrated.
In the cathode underlayer 17, the ratio of the conductive material 45 was gradually decreased from the upper side 17a to the lower side 17b.
Specifically, in the area 34a of the fifth component display unit 34, the proportion of the conductive material 45 was increased to 44 to 73 wt%.
Furthermore, in the area 34b of the fifth component display unit 34, the proportion of the conductive material 45 is 37 to 44 wt%, which is smaller than the proportion of the area 34a.
In addition, in the area 34c of the fifth component display unit 34, the ratio of the conductive material 45 is set to 15 to 37 wt%, which is smaller than the ratio of the area 34b.

Next, in (b), the third component display part 32 of the water repellent material 46 will be described.
Part of the produced water on the cathode side is evaporated in the oxygen gas flow path 24 (see FIG. 4) and moves together with the oxygen gas.
The oxygen gas tends to stay in the bent portions 24c and 24c (see FIG. 4) of the oxygen gas flow path 24, and the flow rate of the oxygen gas decreases on the discharge side 24b (see FIG. 4) of the oxygen gas flow path 24. It's easy to do.
Therefore, the generated water tends to accumulate on the discharge side 24 b of the oxygen gas flow path 24.

For this reason, it is necessary to increase the drainage of the generated water on the discharge side 24b of the oxygen gas flow path 24 and to drain the generated water efficiently.
Therefore, the ratio of the water repellent material 46 is gradually increased from the supply side 24a of the oxygen gas flow path 24 toward the discharge side 24b.

Specifically, in the area 32a of the third component display part 32, the ratio of the water repellent material 46 was reduced to 27 to 56 wt%.
Further, in the area 32b of the third component display section 32, the ratio of the water repellent material 46 is set to 56 to 63 wt%, which is larger than the ratio of the area 32a.
In addition, in the area 32c of the third component display unit 32, the ratio of the water repellent material 46 is set to 63 to 85 wt%, which is larger than the ratio of the area 32b.

Next, in FIG. 6B, the sixth component display portion 35 of the conductive material 45 will be described.
The supply side 24a of the oxygen gas flow path 24 (see FIG. 3) is located on the upper side 17a of the cathode base layer 17, and the discharge side 24b is located on the lower side 17b.
Accordingly, the amount of oxygen (O ₂ ) entering the cathode underlayer 17 through the cathode diffusion layer 18 gradually decreases from the upper side 17a to the lower side 17b of the cathode underlayer 17.

Thereby, the reaction between hydrogen ions (H ⁺ ) and oxygen (O ₂ ) is gradually suppressed from the upper side to the lower side of the cathode catalyst layer 16.
Accordingly, the proportion of the conductive material 45 in the cathode underlayer 17 is changed from the supply side 24a to the discharge side 24b of the oxygen gas flow path 24 in accordance with the reaction state of hydrogen ions (H ⁺ ) and oxygen (O ₂ ). Gradually decreased toward.

Specifically, in the area 35a of the sixth component display unit 35, the ratio of the conductive material 45 was increased to 44 to 73 wt%.
Furthermore, in the area 35b of the sixth component display unit 35, the proportion of the conductive material 45 is 37 to 44 wt%, which is smaller than the proportion of the area 35a.
In addition, in the area 35c of the sixth component display unit 35, the ratio of the conductive material 45 is set to 15 to 37 wt%, which is smaller than the ratio of the area 35b.

Next, the operation of the membrane electrode assembly 12 of the fuel cell provided with the cathode underlayer 17 will be described with reference to FIGS.
FIG. 6 is a diagram for explaining the operation relating to the first component display unit of the first embodiment.
Oxygen (O ₂ ) enters the cathode catalyst layer 16 through the cathode diffusion layer 18 and the cathode base layer 17 as indicated by an arrow c, and the oxygen (O ₂ ) that has entered enters the electrolyte membrane 15 from the cathode catalyst layer 16.
On the other hand, hydrogen ions (H ⁺ ) generated by the reaction in the anode catalyst layer 21 (see FIG. 2) permeate the electrolyte membrane 15 and enter the cathode catalyst layer 16 side as indicated by an arrow d.
Therefore, hydrogen ions (H ⁺ ) and oxygen (O ₂ ) react to generate product water.

Here, in the area 30a of the first component display unit 30, the ratio of the water repellent material 46 was reduced to 27 to 49 wt% to suppress drainage.
Therefore, when hydrogen ions (H ⁺ ) and oxygen (O ₂ ) react and the generated water enters the cathode underlayer 17 as indicated by arrow e, a part of the generated water is converted into the cathode catalyst layer. 16 is returned to the electrolyte membrane 14 side as shown by an arrow f.
Thereby, the electrolyte membrane 15 can be kept in a suitable wet state, and the reaction between hydrogen ions (H ⁺ ) and oxygen (O ₂ ) can be further promoted.

Furthermore, the ratio of the water repellent material 46 was 49 to 73 wt% in the area 30 b of the first component display unit 30 and 73 to 85 wt% in the area 30 c. That is, the ratio of the water repellent material 46 was gradually increased toward the cathode diffusion layer 18 side.
The generated water that has entered the cathode underlayer 17 can be efficiently released as indicated by g toward the cathode diffusion layer 18 side.

FIG. 7 is a diagram for explaining the operation relating to the second component display unit of the first embodiment.
The generated water in the cathode underlayer 17 flows into the cathode diffusion layer 18 as indicated by an arrow g, and the other generated water descends in the cathode underlayer 17 as indicated by an arrow h by its own weight.
Therefore, in the vicinity of the upper side 17a of the cathode base layer 17, the amount of generated water flowing out to the cathode diffusion layer 18 side is relatively small. For this reason, even if the ratio of the water repellent material 46 is reduced to 27 to 56 wt% in the area 31a of the second component display portion 31, the generated water does not accumulate in the upper side 17a and can be discharged to the cathode diffusion layer 18. it can.

On the other hand, as the generated water descends as shown by the arrow h, the amount of generated water tends to increase as it approaches the lower side 17b of the cathode underlayer 17.
Therefore, the ratio of the water repellent material 46 is 56 to 63 wt% in the area 31 b of the second component display unit 31 and 63 to 85 wt% in the area 31 c. That is, the ratio of the water repellent material 46 was gradually increased toward the lower side 17b.
Thereby, the generated water that has reached the lower side 17b of the cathode underlayer 17 can be efficiently discharged from the lower side 17b to the cathode diffusion layer 18 as indicated by an arrow i.

FIG. 8 is a diagram for explaining the operation relating to the third component display unit of the first embodiment.
A part of the generated water in the cathode underlayer 17 is evaporated in the oxygen gas flow path 24 and moves together with the oxygen gas.
Here, oxygen gas flows relatively smoothly on the supply side 24 a of the oxygen gas flow path 24. Therefore, in the supply side 24a of the oxygen gas flow path 24, the generated water can be guided toward the discharge side 24b.
For this reason, even if the ratio of the water repellent material 46 is reduced to 27 to 56 wt% in the area 32 a of the third component display section 32, the cathode diffusion does not accumulate in the supply side 24 a of the oxygen gas flow path 24. The layer 18 can be discharged.

On the other hand, oxygen gas tends to stay in the bent portion 24 c of the oxygen gas flow path 24, and the oxygen gas flow rate tends to decrease on the discharge side 24 b of the oxygen gas flow path 24. Therefore, the generated water tends to accumulate on the discharge side 24 b of the oxygen gas flow path 24.
Therefore, the ratio of the water repellent material 46 is set to 56 to 63 wt% in the area 32 b of the third component display unit 32 and 63 to 85 wt% in the area 32 c. That is, the ratio of the water repellent material 46 was gradually increased toward the discharge side 24 b of the oxygen gas flow path 24.
As a result, the drainage of the produced water can be increased on the discharge side 24b of the oxygen gas flow path 24, and the produced water can be drained efficiently.
Next, an example for realizing the first embodiment will be described in the second embodiment.

Second Embodiment In the membrane electrode assembly 12 of the first embodiment, the second layer 44 (see FIG. 3) of the cathode underlayer 17 has been described as the cathode underlayer 17. The membrane electrode assembly 12 of the form will be described as including the first layer 43 (see FIG. 3).
Hereinafter, the membrane electrode assembly 12 of 2nd Embodiment is demonstrated based on FIGS. 9-11 and Table 2. FIG.
In Table 2, the ratio (wt%) of the water absorbing material, the conductive material 45 and the water repellent material 46 indicates the ratio of the solid content in the cathode underlayer 17.

FIG. 9 is a perspective view showing a state in which the cathode base layer of the membrane electrode assembly (second embodiment) of the fuel cell according to the present invention is distinguished into a plurality of portions.
The cathode underlayer 17 is finished in three rows (Y1, Y2, Y3) and three columns (X1, X2, X3) in a side view, and the Z1 region from the cathode catalyst layer 16 side to the cathode diffusion layer 18 side , Z2 region, Z3 region, and Z4 region are shown in a state of being finished. Thereby, the cathode underlayer 17 is cut into 36 parts.

Hereinafter, the components of the Z1, Z2, Z3, and Z4 regions will be described with reference to FIG.
The Z1 region corresponds to the first layer 43 (see FIG. 3), and the Z2, Z3, and Z4 regions correspond to the second layer 44 (see FIG. 3).
In order to distinguish each part of the cathode underlayer 17, for example, the part indicated by “///” is (X1, Y1, Z4), and the other parts are displayed in the same manner.

FIGS. 10A to 10D are first explanatory views showing the ratios of the water repellent material and the conductive material included in the cathode underlayer of the second embodiment. In addition, the components of A to L shown in each part are the components shown in Table 2.
(A) is a Z1 region, and the Z1 region is a region in contact with the cathode catalyst layer 16. In order to secure the adhesive force of the Z1 region to the cathode catalyst layer 16, a water absorbing material is added to the Z1 region. This is because the water absorbing material functions as an adhesive.
As an example of the water-absorbing material, Nafion (registered trademark of DuPont Co., Ltd.) having excellent adhesiveness is applicable.

  Furthermore, in the cathode catalyst layer 16, the generated water moves in the direction of gravity (downward), and the generated water tends to increase below the cathode catalyst layer 16. Therefore, the water absorption material is gradually increased from the upper side to the lower side of the cathode catalyst layer 16 to improve the water absorption at the lower side of the Z1 region.

In addition, the proportion of the conductive pore-forming agent was gradually increased from the upper side 17a to the lower side 17b of the cathode underlayer 17 as the absorbing material increased. Thereby, the diffusibility of oxygen (O ₂ ) when oxygen (O ₂ ) enters the cathode catalyst layer 16 from the cathode underlayer 17 can be ensured.
As an example of the conductive pore-forming agent, acicular carbon fiber having conductivity is applicable.

Specifically, the component was set to A at three sites, ie, site (X1, Y1, Z1), site (X2, Y1, Z1) and site (X3, Y1, Z1).
The component was defined as b at three sites, site (X1, Y2, Z1), site (X2, Y2, Z1) and site (X3, Y2, Z1).
The component was set to c at three sites, site (X1, Y3, Z1), site (X2, Y3, Z1) and site (X3, Y3, Z1).

(B) is the Z2 region, and the site (X1, Y1, Z2), site (X2, Y1, Z2), site (X3, Y1, Z2), site (X3, Y2, Z2) and site (X2, The component was defined as D at 5 sites of Y2, Z2).
The component was defined as E at 4 sites: site (X1, Y2, Z2), site (X1, Y3, Z2), site (X2, Y3, Z2) and site (X3, Y3, Z2).

(C) is the Z3 region, and the component is E in one part of the part (X1, Y1, Z3).
The component was defined as F at three sites: site (X2, Y1, Z3), site (X3, Y1, Z3) and site (X3, Y2, Z3).
The component was defined as G at three sites: site (X2, Y2, Z3), site (X1, Y2, Z3) and site (X1, Y3, Z3).
The component was defined as H at two sites, site (X2, Y3, Z3) and site (X3, Y3, Z3).

(D) is the Z4 region, that is, the region in contact with the cathode diffusion layer 18, and the component is H at one site of the sites (X1, Y1, Z4).
The component was defined as I at two sites, site (X2, Y1, Z4) and site (X3, Y1, Z4).
The component was defined as J at the two sites of site (X3, Y2, Z4) and site (X2, Y2, Z4).

The component was defined as K at the two sites (X1, Y2, Z4) and (X1, Y3, Z4).
The component was defined as L at two sites, site (X2, Y3, Z4) and site (X3, Y3, Z4).

Thereby, the water repellent material of each part which comprises Z2 area | region, Z3 area | region, and Z4 area | region was included so that it might increase gradually from the supply side 24a of the oxygen gas flow path 24 toward the discharge | emission side 24b.
Therefore, a large amount can be contained in a site that requires a large amount of water repellent material, and a small amount can be contained in a site that requires only a small amount.

Further, the water repellent material of each part constituting the Z2, Z3, and Z4 regions was included so as to gradually increase from the upper side 17a to the lower side 17b of the cathode underlayer 17.
Therefore, a large amount can be contained in a site that requires a large amount of water repellent material, and a small amount can be contained in a site that requires only a small amount.
Next, components of the Y1 region, Y2 region, and Y3 region of the cathode underlayer 17 shown in FIG. 9 will be described with reference to FIGS.

FIGS. 11A to 11C are second explanatory views showing the ratio of the water repellent material and the conductive material included in the cathode underlayer of the second embodiment.
(A) is a Y1 region, that is, a region to be an upper portion of the cathode underlayer 17, and the portion (X1, Y1, Z1), the portion (X2, Y1, Z1) and the portion (X3, Y1) on the cathode catalyst layer 16 side. , Z1), the components are all A.
The component was defined as D at 3 sites: site (X1, Y1, Z2), site (X2, Y1, Z2) and site (X3, Y1, Z2).

The component was defined as E at one site (X1, Y1, Z3).
The component was defined as F at two sites, site (X2, Y1, Z3) and site (X3, Y1, Z3).
The component was H at one site (X1, Y1, Z4).
The component was defined as I at two sites, site (X2, Y1, Z4) and site (X3, Y1, Z4).

(B) is a Y2 region, that is, a region that becomes the central portion of the cathode underlayer 17, and the portion (X1, Y2, Z1), the portion (X2, Y2, Z1), and the portion (X3, X) on the cathode catalyst layer 16 side. The components were all B at 3 sites Y2 and Z1).
The component was defined as E at one site (X1, Y2, Z2).
The component was defined as D at two sites, site (X2, Y2, Z2) and site (X3, Y2, Z2).

The component was defined as G at two sites, site (X1, Y2, Z3) and site (X2, Y2, Z3).
The component was F in one site (X3, Y2, Z3).
The component was K at one site (X1, Y2, Z4).
The component was defined as J at the two sites of site (X2, Y2, Z4) and site (X3, Y2, Z4).

(C) is a Y3 region, that is, a region which is a lower portion of the cathode underlayer 17, and is located on the cathode catalyst layer 16 side (X1, Y3, Z1), site (X2, Y3, Z1) and site (X3, Y3). , Z1), all of the components were C.
The components were all E in the three sites of site (X1, Y3, Z2), site (X2, Y3, Z2) and site (X3, Y3, Z2).

The component was G in one site (X1, Y3, Z3).
The component was defined as H at two sites, site (X2, Y3, Z3) and site (X3, Y3, Z3).
The component was K at one site (X1, Y3, Z4).
The component was defined as L at two sites, site (X2, Y3, Z4) and site (X3, Y3, Z4).

Thereby, the water repellent material of each part which comprises Y1 area | region, Y2 area | region, and Y3 area | region was included so that it might increase gradually toward the cathode diffusion layer 18 side from the cathode catalyst layer 16 side.
Therefore, a large amount can be contained in a site that requires a large amount of water repellent material, and a small amount can be contained in a site that requires only a small amount.

By distributing the water repellent material in the cathode underlayer 17 as in the second embodiment described above, the water repellent material is supplied to the supply side 24a of the oxygen gas flow path 24 as in the first embodiment. From the cathode catalyst layer 16 side toward the cathode diffusion layer 18 side and gradually increased from the upper side 17a of the cathode base layer 17 toward the lower side 17b.
Therefore, according to the membrane electrode assembly 12 of the second embodiment, the same effect as that of the first embodiment can be obtained.

  In the above-described embodiment, the electrolyte membrane 15, the cathode / anode side catalyst layers 16 and 21, the cathode / anode side base layers 17 and 22, and the cathode / anode side diffusion layers 18 and 23 act in the direction of gravity. Although the example in which the fuel cell 10 is arranged so that these layers face the vertical direction has been described, the direction of each layer is not limited to the vertical direction. In short, each layer may be arranged so as to face the direction in which gravity acts.

  In the embodiment, the water repellent material 46 is gradually increased from the supply side 24a of the oxygen gas flow path 24 toward the discharge side 24b, and further from the upper side 17a to the lower side 17b of the cathode base layer 17. Although an example in which the three contents of increasing gradually and in addition gradually increasing from the cathode catalyst layer 16 side toward the cathode diffusion layer 18 side has been described, the present invention is not limited to this. The same effect can be obtained by adopting only the contents that are gradually increased from the upper side 17a to the lower side 17b of the foundation layer 17, that is, in the direction in which the gravity acts.

  Further, the water repellent material 46 is gradually increased from the upper side 17a to the lower side 17b of the cathode base layer 17, that is, in the direction in which gravity acts, and from the cathode catalyst layer 16 side to the cathode diffusion layer 18 side. The same effect can be obtained by combining the two contents of increasing gradually.

  Further, the water repellent material 46 is gradually increased from the upper side 17 a to the lower side 17 b of the cathode underlayer 17, that is, in the direction in which gravity acts, and from the supply side 24 a to the discharge side 24 b of the oxygen gas flow path 24. The same effect can be obtained by combining the two contents of increasing gradually toward the.

  The membrane electrode assembly of the present invention is suitable for application to a fuel cell in which hydrogen gas is supplied to the anode side and oxygen gas is supplied to the cathode side to generate electric power.

1 is a perspective view showing a fuel cell provided with a membrane electrode assembly (first embodiment) according to the present invention. It is sectional drawing of the membrane electrode assembly (1st Embodiment) of the fuel cell which concerns on this invention. FIG. 3 is a three-part enlarged view of FIG. 2. It is explanatory drawing which shows the component ratio which comprises the cathode base layer of 1st Embodiment. It is explanatory drawing which shows the ratio of the water repellent material and electroconductive material which are contained in the cathode base layer of 1st Embodiment. It is a figure explaining the effect | action regarding the 1st component display part of 1st Embodiment. It is a figure explaining the effect | action regarding the 2nd component display part of 1st Embodiment. It is a figure explaining the effect | action regarding the 3rd component display part of 1st Embodiment. It is a perspective view which shows the state which distinguished the cathode base layer of the membrane electrode assembly (2nd Embodiment) of the fuel cell which concerns on this invention into the some site | part. It is 1st explanatory drawing which shows the ratio of the water repellent material and electrically conductive material which are contained in the cathode base layer of 2nd Embodiment. It is 2nd explanatory drawing which shows the ratio of the water repellent material and electroconductive material which are contained in the cathode base layer of 2nd Embodiment. It is a figure explaining the principal part of the membrane electrode assembly of the conventional fuel cell. It is sectional drawing which shows the principal part of the membrane electrode assembly of the conventional fuel cell. It is a side view which shows the principal part of the membrane electrode assembly of the conventional fuel cell.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Fuel cell, 12 ... Fuel cell membrane electrode assembly, 15 ... Electrolyte membrane, 16 ... Cathode catalyst layer, 17 ... Cathode base layer, 18 ... Cathode diffusion layer, 45 ... Conductive material, 46 ... Water-repellent material, 24 ... oxygen gas flow path, 24a ... supply side of oxygen gas flow path, 24b ... discharge side of oxygen gas flow path.

Claims (2)

A cathode catalyst layer, a cathode underlayer, and a cathode diffusion layer are laminated on the cathode side of the electrolyte membrane, and an oxygen gas flow path is provided outside the cathode diffusion layer, and each layer and the electrolyte membrane are directed in the direction in which gravity acts. In the fuel cell membrane electrode assembly to be arranged,
A membrane electrode assembly for a fuel cell, wherein the cathode underlayer includes a conductive material and a water repellent material, and the proportion of the water repellent material is gradually increased in a direction in which gravity acts. The ratio of the water repellent material is increased from the cathode catalyst layer side toward the cathode diffusion layer side and / or gradually increased from the supply side to the discharge side of the oxygen gas flow path. The membrane electrode assembly of the fuel cell according to claim 1.

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