JP2001006708A - Solid high polymer fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep a wet condition throughout a solid high polymer film area even if an oxidizer gas which is not humidified is supplied, by lowering moisture permeability of a gas diffusion layer on a cathode side in the neighboring area of a gas inlet than moisture permeability of a gas diffusion layer on an anode side in other areas. SOLUTION: This high polymer fuel cell is formed by interveningly inserting a solid high polymer film 21 between a cathode 22 and an anode 23 and sandwiching them by two diffusion layers, and electricity is generated by passing an oxidizing gas and a fuel gas through it. In the gas diffusion layer 24 on the cathode 22 side of the cell 20, a fluorine resin content in the front part 241 forming the neighboring area of an air inlet is made bigger than that in the back part 242 forming the neighboring area of an air outlet, and high water repellency is given to the front part. Moisture evaporation in a solid high polymer film 21 area corresponding to the front part 241 is suppressed, conductivity of the solid high polymer film 21 is uniformed, and excellent power generation effect is displayed under good stability. A structure having a thick gas diffusion layer so as to make the moisture permeability low in the neighboring area of the gas inlet on the cathode 22 side is also preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer electrolyte fuel cell, and more particularly to an improved technique for maintaining the wettability of a solid polymer membrane in a cell.

[0002]

2. Description of the Related Art A fuel cell supplies a hydrogen-rich fuel gas to an anode side and an oxidant gas to a cathode side, respectively.
This is a battery that generates electricity by electrochemically reacting hydrogen and oxygen. Air is often used as the oxidant gas. As the fuel gas, a light hydrocarbon such as natural gas or naphtha, a gas obtained by reforming a fuel gas composed of a lower alcohol, or pure hydrogen gas is used.

There are various types of fuel cells depending on the type of electrolyte, such as a phosphoric acid type and a molten carbonate type. In recent years, research on solid polymer type fuel cells using a solid polymer membrane as an electrolyte has been actively made. I have. This polymer electrolyte fuel cell
The solid polymer membrane has a basic structure in which a cell having a cathode on one surface and an anode on the other surface is sandwiched between gas diffusion layers. In a practical polymer electrolyte fuel cell, such a basic structure is used as a unit cell, and a large number of such cells are stacked to obtain high output.

[0004]

Generally, in a polymer electrolyte fuel cell, it is desirable that the solid polymer membrane be wet in order to improve power generation efficiency. This is because the internal resistance of the solid polymer film is reduced, ions are easily moved, and power generation efficiency is improved. Therefore, measures such as supplying a humidified oxidant gas to the fuel cell in advance have been taken.

[0005] However, in recent years, there has been a demand for a more compact fuel cell system, which requires a reduction in system elements for humidifying the oxidizing gas. There is a tendency to supply batteries. However, in polymer electrolyte fuel cells, the humidity of the oxidizing gas near the gas inlet on the cathode side tends to be lower than the humidity near the gas outlet,
In the vicinity of the gas inlet on the cathode side, a relatively large amount of moisture evaporates into the oxidizing gas from the solid polymer membrane, and there is a possibility that the power generation efficiency of the fuel cell may be reduced in this portion. In particular, when a non-humidified oxidizing gas is supplied, the effect of the above problem is expected to increase, and it is necessary to immediately take measures for it.

As described above, it is considered that there is still room for technical improvement in order to achieve both miniaturization of the polymer electrolyte fuel cell and maintenance of the power generation efficiency thereof. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a stable power generation by keeping a solid polymer membrane in a wet state even when a non-humidified oxidizing gas (air) is supplied. To provide a polymer electrolyte fuel cell that can be used.

[0007]

In order to solve the above-mentioned problems, the present invention comprises inserting a solid polymer membrane between a cathode and an anode,
It has a cell configuration in which this is sandwiched between two gas diffusion layers, and an oxidizing gas flows along the surface of the gas diffusion layer on the cathode side, and a fuel gas flows along the surface of the gas diffusion layer on the anode side. A polymer electrolyte fuel cell that generates power by means of a structure in which the water permeability of the gas diffusion layer on the cathode side near the gas inlet is lower than the water permeability of the gas diffusion layer on the cathode side in other areas did.

[0008] This makes it possible to suppress the tendency of moisture from the solid polymer film to be easily lost in the vicinity of the oxidant gas inlet, thereby making the wettability of the solid polymer film uniform. Specifically, the thickness of the gas diffusion layer on the cathode side can be configured to increase along the direction from the vicinity of the gas outlet to the vicinity of the gas inlet.

As described above, when a thick gas diffusion layer is arranged near the gas inlet on the cathode side so as to reduce the moisture permeability, the moisture of the solid polymer membrane from this portion moves to the surface of the gas diffusion layer. It is difficult to suppress excessive water evaporation of the solid polymer film. As a result, the conductivity of the solid polymer film is maintained, and stable power generation is performed. Further, in addition to changing the thickness of the gas diffusion layer, the water repellent content of the gas diffusion layer on the cathode side increases along the direction from the vicinity of the gas outlet to the vicinity of the gas inlet. Can also. Thereby, substantially the same effects as described above can be obtained.

[0010]

(Embodiment 1) Hereinafter, Embodiment 1 of a polymer electrolyte fuel cell according to the present invention will be described. The main feature of the present invention resides in a cell configuration centered on a solid polymer film, and other components are common to the following embodiments. Therefore, here, the basic configuration of the polymer electrolyte fuel cell will be described first, and then the cell configuration will be described in detail. In the second and subsequent embodiments, descriptions overlapping with the first embodiment will be omitted. <Cell Unit Configuration of Polymer Electrolyte Fuel Cell> FIG.
FIG. 2 is an assembly diagram of the cell unit 10 constituting the polymer electrolyte fuel cell according to the first embodiment. As shown in the figure, the cell unit 10 has a configuration in which the cell 20 is sandwiched between a cathode-side channel plate 60 and an anode-side channel plate 50 as a whole.

The cell 20 comprises a solid polymer film 21, a cathode 2
2, the anode 23, the gas diffusion layers 24 and 25, and the like. The solid polymer film 21 is made of a thin film electrolyte made of perfluorocarbon sulfonic acid (for example, Nafio manufactured by Du Pont).
n112). The cathode 22 and the anode 23 are films made of platinum (Pt) -supported carbon or the like, and are tightly processed by hot pressing at the center of both main surfaces of the solid polymer film 21. The cathode 22 and the anode 23 are also called a catalyst layer.

In FIG. 1, since the anode 23 is on the lower surface side of the solid polymer film 21, it is indicated by a broken line. The cathode 22 side of the cell 20 is placed on the cathode side channel plate 60 via the gasket 40. The anode 23 side is overlapped on the anode side channel plate 50 via the gasket 30.

At this time, between the cathode 22 and the cathode side channel plate 60 and between the anode 23 and the anode side channel plate 50, a gas diffusion layer 24 made of carbon paper impregnated with, for example, PTFE as a water repellent, 25 are inserted respectively. These gas diffusion layers 24 and 25 are also called current collectors. The anode-side channel plate 50 is a member formed by injection-molding a mixture of phenolic resin and carbon powder. On the surface (the lower surface in FIG. 1) facing the gas diffusion layer 25, the y-direction is the longitudinal direction and the x-direction Ribs 56 are juxtaposed at regular intervals, thereby forming a channel 55 for flowing a hydrogen-rich reformed gas (fuel gas) in the same direction.

The cathode-side channel plate 60 is substantially the same as the anode-side channel plate 50. Although not visible in FIG. 1, ribs are arranged at regular intervals in the x direction with the y direction as the longitudinal direction. Thus, a channel for flowing air in the same direction is formed. The solid polymer membrane 21, gaskets 30, 40, anode-side channel plate 50, and cathode-side channel plate 60 have openings 61-64, 41-44, 211-
214, 31-34, 51-54 (44, 214, 3
4 and 54 are not shown).
1, 53, 31, 33, 211, 213, 41, 43,
Fuel gas is supplied to the channels 55 of the anode-side channel plate 50 by 61 and 63. The opening 5
2, 54, 32, 34, 212, 214, 42, 44,
Air is supplied to the channels of the cathode side channel plate 60 by 62 and 64.

In the cell unit 10 having such a configuration, a plurality of sets are stacked via a partition plate so that high voltage and high power can be actually taken out, and both ends thereof are sandwiched between a pair of end plates. Is fixed and assembled as one fuel cell. Here, the main feature of the first embodiment lies in the configuration centering on the cell 20. Next, the configuration of the cell 20 will be described in detail.

<Cell Configuration> FIG. 2 is a sectional view of the cell 20 cut in the thickness direction (yz plane). Here, the solid polymer film 21 is the center, the cathode 22, the anode 23,
The gas diffusion layers 24 and 25 are illustrated. The size of each of these elements 21 to 25 is the same as the conventional one, for example, as shown below. Solid polymer film 21; width 12 cm in x direction × length 12 in y direction
cm × z direction thickness about 50 μm cathode 22, anode 23; x direction width 10 cm × y direction length 10 cm × z direction thickness about 20 μm gas diffusion layers 24 and 25; x direction width 10 cm × y direction length 10 cm × z In the cell 20, in the gas diffusion layer 24 on the cathode 22 side, the fluorine resin content of the front portion 241 near the air inlet to the cathode-side channel plate 60 (near the opening 62) is reduced. More (for example, about twice) than the rear portion 242 which is a region near the air discharge port (near the opening 64),
Thus, the front portion 241 is configured to have relatively high water repellency. The area of the front portion 241 occupies 50% (50 cm ² ) of the entire gas diffusion layer 24 as an example here.

According to the cell 20 having such a configuration, when the fuel cell is operated, the anode 2 is connected via the gas diffusion layer 25.
Hydrogen in the fuel gas supplied to the third side is ionized to protons (H ₂ → 2H ⁺ + 2e ⁻ ), and the solid polymer membrane 21
The inside moves to the cathode 22 side. On the other hand, the gas diffusion layer 24
The oxygen in the air supplied to the cathode 22 via the oxygen becomes oxygen ions (1 / 2O ₂ + 2e ⁻ → O ²⁻ ), and combines with the protons moving in the solid polymer membrane 21 to generate water ( 2H ⁺ + O ^2- → H ₂ O).

The solid polymer film 21 is formed by this chemical mechanism.
Becomes wet, and the internal resistance is lowered to exhibit conductivity. By the way, conventionally, during operation of such a fuel cell, in the front part 241 of the gas diffusion layer 24, the moisture of the solid polymer film 21 excessively evaporates, and the solid polymer film near the region corresponding to the front part 241 Tended to lose wettability and decrease in conductivity, adversely affecting power generation efficiency. Even if the air supplied to the cell unit 10 is humidified in advance, such a tendency is likely to occur because the humidity is still low at first, and there is a tendency that the humidified air is particularly remarkable when the air is supplied without humidification.

On the other hand, in the first embodiment, the front portion 24
1 has a high fluororesin content in the gas diffusion layer 24 and a high water repellency to reduce the moisture permeability, so that the moisture in the region of the solid polymer film 21 corresponding to the front part 241 evaporates. Attempting to do so is sufficiently suppressed. As a result, the conductivity of the solid polymer film 21 is made uniform,
It is possible to exhibit excellent power generation efficiency under good stability.

The excellent performance of the first embodiment is expected to be particularly effective in a fuel cell system in which external air is supplied to the cell unit 10 in a non-humidified state, for example, in which moisture is likely to evaporate. You. The gas diffusion layer 2
The ratio of the area of the front portion 241 to the area 4 is not limited to the above value, but may be naturally adjusted according to the operating conditions. For example, when the temperature of the cell unit during operation of the fuel cell is high, the amount of water evaporation tends to increase, so it may be desirable to increase the area of the front part where the fluorine resin content is increased.

The fluorine resin content in the gas diffusion layer 24 may be configured to gradually decrease from the front part 241 to the rear part 242. Hereinafter, another embodiment of the present invention will be described. Second Embodiment <Cell Configuration> In the first embodiment, the content of the fluororesin in the gas diffusion layer 24 is increased in the front part 241 to increase the solid polymer film 2.
In the second embodiment, the thickness of the gas diffusion layer 24 is larger than that of the rear part 242, but the thickness of the gas diffusion layer 24 is smaller than that of the front part 242.
The feature is that the thickness is increased by 1.

FIG. 3 is a cross-sectional view of the cell 20 according to the second embodiment cut in the thickness direction (yz plane). The gas diffusion layer 24 has a uniform fluorine resin content (density per volume of the gas diffusion layer 24), but the thickness thereof is
2 to the front 241 and gradually increasing slope (50
μm → 70 μm). Other configurations are the same as those in the first embodiment.

According to the cell 20 having such a configuration, since the thickness of the gas diffusion layer 24 is relatively thick at the front part 241, the water content of the solid polymer film 21 corresponding to the front part 241 becomes smaller than before.
It is difficult to move to the surface of the gas diffusion layer 24 via the cathode 22, and the amount of water evaporation is suppressed. Thereby, the wettability of the solid polymer film 21 is kept uniform, and good conductivity is maintained.

Although FIG. 3 shows an example in which only the thickness of the gas diffusion layer 24 on the cathode 22 side is changed, the present invention is not limited to this, and the thickness of the gas diffusion layer 25 on the anode 23 side is further changed. May be changed.
Here, FIG. 4 shows the thickness of the anode 23 along the y direction.
It shows an example in which the thickness is gradually increased (variation 1). Here, the thickness of the gas diffusion layer 24 together with the anode 23 is changed so that the cross-sectional shape of the cell 20 is a parallelogram, and the thickness of the cell 20 is constant (210 μm). In this way, when assembled as the cell unit 10, even if a plurality of the cell units 10 are stacked, the thickness does not become uneven.

FIG. 5 shows an example (variation 2) in which the thickness of the gas diffusion layer 25 is gradually increased along the y direction. In the present invention, as described above, the anode 2 is adjusted in accordance with the adjustment of the thickness of the gas diffusion layer 24.
3 or the thickness of the gas diffusion layer 25 may be changed. Further, the thickness may be changed in a stepped shape or a curved shape in addition to the linear gradient shown in the second embodiment.

Although not shown, Embodiments 1 and 2 may be combined to increase the thickness of the front portion 241 while increasing the fluorine resin content of the front portion 241 compared to other regions. (Performance Comparison Experiment) In order to confirm the performance of the polymer electrolyte fuel cell of the present invention, the cells (single cells) described in each embodiment, that is, Embodiment 1, Embodiment 2, Variation 1, Variation 2 And a power generation test was performed.

As the single cell of the first embodiment, four types were prepared by changing the fluorine resin content in the front part and the rear part of the gas diffusion layer on the cathode side, and these were used as cells 1 to 4. As comparative examples, two kinds of gas diffusion layers having a constant fluorine resin content in the gas diffusion layer on the cathode side were prepared, and these were used as cells 5 and 6.
And The specific manufacturing method of the cells 1 to 4 is as follows.

<Method for Manufacturing Single Cell of First Embodiment> 1. Preparation of Materials Solid polymer membrane; perfluorocarbon sulfonic acid membrane (Na
fion112 film, length 12cm x width 12cm x thickness 50μ
m) Gas diffusion layer on cathode side; carbon paper (thickness 20)
0 μm) is prepared, and an area (5 cm long) corresponding to this front part is prepared.
× 10 cm) was sprayed with a fluororesin (PTFE) dispersion solution. And the carbon paper is made of fluororesin (P
After being immersed in the TFE) dispersion solution, it was baked at 380 ° C. for 1 hour. Thereby, the fluororesin content in the front part is 2
Each gas diffusion layer having 6, 30, 50, 60 wt% and a fluorine resin content of 25 wt% in the rear portion was prepared.

A gas diffusion layer on the anode side; a carbon paper (thickness: 200 μm) was prepared, and a fluororesin (PTF) was prepared.
E) After immersion in the dispersion solution, it was baked at 380 ° C. for 1 hour. Thus, an anode-side gas diffusion layer having a fluorine resin content of 25 wt% was produced. Cathode and anode; Pt-supported carbon powder, Nafi
on solution, PTFE dispersion solution, Pt-supported carbon powder: N
The weight ratio of afion: PTFE was mixed at a ratio of 100: 20: 10, and the resulting slurry was applied to the gas diffusion layer at a thickness of 20 μm to form a cathode and an anode.

2. Hot Press Step A solid polymer film was inserted between the two gas diffusion layers coated with the catalyst layers, and hot pressed at 150 ° C. for 60 seconds.
Through these steps, cells 1 to 6 were produced. The gas diffusion layers of the cells 5 and 6 are made of carbon paper made of PT.
Except for spraying the FE dispersion solution, it was prepared in the same manner as the gas diffusion layer on the cathode side of cells 1 to 4.

Table 1 shows the specifications of these cells 1 to 6.

[0032]

[Table 1]

Next, as a single cell of the second embodiment, the thickness of the front end and the rear end of the gas diffusion layer on the cathode side was changed to 4
These were prepared and used as cells 7 to 10. As comparative examples, two kinds of gas diffusion layers having a constant thickness of the cathode side gas diffusion layer were produced, and these were used as cells 11 and 12.

The specific manufacturing method of the cells 7 to 10 is as follows. <Method of Manufacturing Single Cell of Second Embodiment> 1. Preparation of Materials Solid polymer membrane; perfluorocarbon sulfonic acid membrane (Na
fion112 film, length 12cm x width 12cm x thickness 50μ
m) Gas diffusion layer on the cathode side: A slurry was prepared by mixing carbon black and PTFE so that PTFE occupied 25 wt%, and screen-printed on a Teflon sheet. At this time, the gradient of the thickness of the gas diffusion layer was adjusted by gradually reducing the area of the slurry overcoating along the longitudinal direction of the gas diffusion layer. After the slurry is dried, it is peeled off from the Teflon sheet and baked at 380 ° C. for 1 hour. And

Gas diffusion layer on anode side; thickness 50 μm
A gas diffusion layer was prepared in the same manner as the cathode side gas diffusion layer except that the gas diffusion layer was made uniform. Cathode and anode; produced in the same manner as the cathode and anode of cells 1 to 6. 2. Hot pressing step A hot pressing step was performed in the same manner as in the case of cells 1 to 6.

Table 2 shows the specifications of these cells 7 to 12.

[0037]

[Table 2]

Next, as single cells of variations 1 and 2, two types of cells were prepared by changing the thickness of the gas diffusion layer on the cathode side and the thickness of the anode or the gas diffusion layer on the anode side. 1
3 (variation 1) and cell 14 (variation 2).

The specific manufacturing method of the cells 13 and 14 is as follows. <Methods for Fabricating Single Cells of Variations 1 and 2> 1. Preparation of Materials (Cell 13) Solid polymer membrane; Perfluorocarbon sulfonic acid membrane (Na
fion112 film, length 12cm x width 12cm x thickness 50μ
m) Cathode-side gas diffusion layer: A slurry was prepared in the same manner as in cells 7 to 12, and screen-printed on a Teflon sheet.
At this time, the gradient of the thickness of the gas diffusion layer was adjusted by gradually reducing the area of the slurry overcoating along the longitudinal direction of the gas diffusion layer. After drying the slurry, it was peeled off from the Teflon sheet and baked at 380 ° C. for 1 hour to form a cathode-side gas diffusion layer having a front part thickness of 70 μm and a rear part thickness of 50 μm (length 10 cm × width 10 cm).

Gas diffusion layer on anode side; thickness 50 μm
A gas diffusion layer was prepared in the same manner as the cathode side gas diffusion layer except that the gas diffusion layer was made uniform. Cathode: produced in the same manner as in cells 1 to 6. Anode; Pt @ Ru supported carbon powder, Nafion solution,
The PTFE dispersion solution was mixed at a predetermined ratio, and the weight ratio of Pt @ Ru-supported carbon powder: Nafion: PTFE was 100:
The slurry adjusted to 20:10 was applied to the gas diffusion layer to form an anode. At this time, the anode was coated such that the front end thickness was 20 μm and the rear end thickness was 40 μm.

(Cell 14) Solid polymer membrane; Perfluorocarbon sulfonic acid membrane (Na
fion112 film, length 10cm × width 10cm × thickness 50μ
m) Cathode-side gas diffusion layer: A slurry was prepared in the same manner as in cells 7 to 12, and screen-printed on a Teflon sheet.
At this time, the gradient of the thickness of the gas diffusion layer was adjusted by gradually reducing the area of the slurry overcoating along the longitudinal direction of the gas diffusion layer. After drying the slurry, it was peeled off from the Teflon sheet and baked at 380 ° C. for 1 hour to form a cathode-side gas diffusion layer having a front part thickness of 70 μm and a rear part thickness of 50 μm (length 10 cm × width 10 cm).

Anode-side gas diffusion layer: A slurry is prepared in the same manner as the cathode-side gas diffusion layer, and is repeatedly screen-printed on a Teflon sheet to form a front part along the longitudinal direction of the cathode-side gas diffusion layer. Is 30μ thick
m, an anode-side gas diffusion layer having a rear thickness of 50 μm. Cathode and anode; Pt @ Ru supported carbon, Na
fion112 solution, PTFE in a weight ratio of 100: 20: 10
And applied to the gas diffusion layer at a thickness of 20 μm to form a cathode and an anode.

2. Hot Press Step A hot press step was performed in the same manner as in the case of cells 1 to 6. Table 3 shows the specifications of these cells 13 and 14.

[0044]

[Table 3]

The cells 1 to 14 thus manufactured were operated under the following conditions, and the change over time in the cell voltage was examined. (Operating conditions) Current density: 0.5 A / cm ² , operating temperature in the cell: 80 ° C. Fuel gas: pure hydrogen Oxidizing gas; air Fuel gas utilization rate: 70% Oxidizing gas utilization rate: 40% In addition, a test operation was carried out for the samples 14 and 14 for a change in cell voltage due to a difference in fuel gas described later. Pure hydrogen and a reforming simulation gas (H ₂ ; 80%, CO ₂ ; 20%, CO; 50 ppm) were used as the fuel gas, and the other conditions were the same as above. The relationship between the cell voltage of each of the cells 1 to 14 and the operating time obtained under the above operating conditions is summarized in FIG. 6 and FIG. FIG. 6 shows cells 1 to 6,
FIG. 7 shows data of cells 7-14.

Table 4 summarizes the results of experiments on the cell voltages of the cells 13 and 14 due to the difference in fuel gas. These will be considered sequentially. First, from FIG. 6, cells 1 to 4 in which the fluorine resin content in the gas diffusion layer on the cathode side was larger in the front part than in the rear part were operated for a longer time than cells 5 and 6 in which the fluorine resin content was constant. However, it can be seen that it has excellent cell voltage stability. This confirms that in the front part of the gas diffusion layer on the cathode side, excessive moisture evaporation from the solid polymer membrane was suppressed by the abundant fluororesin in the gas diffusion layer, and the conductivity of the membrane was maintained uniformly. It seems to be something.

Further, in FIG. 6, the reason why the characteristics of the cells 3, 4, and 6 exhibiting a constant cell voltage value irrespective of the elapse of the operation time can be inferred as follows. The fluorine resin contained in the gas diffusion layer on the cathode side shows higher water repellency to the solid polymer film as its content increases, and the wettability of the solid polymer film can be secured, but the fluorine resin is not so much When the amount increases, the gas diffusibility of the layer decreases, and the oxidizing gas is not supplied to the cathode satisfactorily.

Therefore, among the cells 3, 4, and 6 having a gas diffusion layer having a high fluororesin content, the cell 6 having a uniformly high fluororesin content in the gas diffusion layer has a wettability of the solid polymer film. Is maintained, the cell voltage is stable, but the voltage value is not so excellent. On the other hand, in the cells 3 and 4 corresponding to the first embodiment, since the fluororesin content decreases from the front part to the rear part of the gas diffusion layer, the oxidizing gas is appropriately contained in the gas diffusion layer. The balance between the wettability of the supplied solid polymer membrane and the amount of gas supply is shown, and the relatively high cell voltage and the ideal result with respect to its stability are exhibited.

From this figure, it can be seen that although the cell 1 is an example of the embodiment of the present invention, the performance tends to be slightly lower than those of the other embodiments. It can be seen that the cell voltage is slightly lower than that of the cell 5 of the comparative example. Accordingly, it can be said that the fluororesin content of the gas diffusion layer is particularly preferably such that the ratio of the front part / rear part is within the range of 1.05 to 2.00.

If the fluorine resin content in the front part of the gas diffusion layer on the cathode side is less than 15 wt%, sufficient water repellency cannot be obtained, and if it exceeds 90 wt%, gas diffusivity is extremely lost. Other experiments have shown the effect. From this, the fluorine resin content in the front part of the gas diffusion layer on the cathode side is 15 to 90 watts.
A range of t% is considered desirable.

Next, look at FIG. Here, cell 7 and subsequent 1
The data of the test operation up to 4 are shown. In this figure, the cell voltage shows a constant value regardless of the operation time.
Cells 9, 10, 12, etc. can be seen. Cell 12 is a conventional comparative example, in which the gas diffusion layer on the cathode side is uniformly uniform.
It has a thickness of 00 μm. For this reason, the thickness of the gas diffusion layer is too large as a whole, and the supply of the oxidizing gas to the cathode side cannot be performed well. As a result, the wettability of the solid polymer film is maintained, but a low cell voltage is exhibited. .

On the other hand, in the cells 9 and 10 corresponding to the second embodiment, the thickness of the gas diffusion layer on the cathode side decreases from the front end to the rear end. It is presumed that the balance between the wettability of the solid polymer membrane and the gas supply amount was obtained in the same manner as described above, and the solid polymer membrane had good performance. The cell 11 has a gas diffusion layer almost similar to the conventional one, and it is considered that the power of the solid polymer membrane evaporates rapidly from the front of the gas diffusion layer on the cathode side as the operation time elapses, and the power generation efficiency decreases. It is.

Also, from this figure, all of the cells 8, 13 and 14 show almost the same high cell voltage and stability. The thickness of the gas diffusion layer on the cathode side is changed, and the gas diffusion on the anode or the anode side is changed. It is shown that the effect of the present invention can be obtained even when the thickness of the cell is kept constant by changing the thickness of the layer. Here, from this figure, although the cell 7 is an example of the embodiment of the present invention, the performance tends to slightly decrease over time as compared with the examples of the other embodiments. It can be seen that the cell voltage is low. Thereby, the thickness of the gas diffusion layer is such that the ratio of the front part / rear part is 1.05.
It can be said that a value falling between 2.00 and 2.00 is particularly desirable.

Next, the experimental data in Table 4 will be considered. Table 4 is shown below.

[0055]

[Table 4]

In each of the cells 13 and 14, Pt @ Ru-supported carbon is used as a cathode and anode catalyst. Of these, Pt exhibits a good catalytic action when pure hydrogen is used as the fuel gas, but if the fuel gas contains carbon monoxide CO, it may be poisoned and the catalytic action may be reduced. On the other hand, Ru is not considered to be as poisonous as CO as Pt.

Table 4 seems to indicate a change in the cell voltage value due to such Pt poisoning. That is, when pure hydrogen is used as the fuel gas, both the cells 13 and 14 show a high cell voltage value. However, when the reforming simulated gas is used, the Pt poisoning action of CO contained therein causes The cell voltage at 14 drops. Since the cell 13 has a configuration in which the thickness of the anode is adjusted according to the change in the thickness of the gas diffusion layer on the cathode side, the amount of catalyst increases in proportion to the thickness of the anode. Since the cell 14 has a configuration in which the thickness of the gas diffusion layer on the anode side is adjusted according to the change in the thickness of the gas diffusion layer on the cathode side, the amount of catalyst on the anode is smaller than that of the cell 13. It is considered that the result shown in FIG.

According to such an experiment, when the cell units are stacked and the reformed gas containing CO is used as the fuel gas, the cell unit of the polymer electrolyte fuel cell according to the present invention is a variation 1 corresponding to the cell 13. It can be said that the following configuration is desirable. In addition, PTF is used as the water repellent of the gas diffusion layer.
Fluororesins other than E and other materials may be used as appropriate.

In each of the above embodiments and variations, the description has been given based on the cell unit in which the flows of the oxidizing gas and the fuel gas are parallel. However, the configuration of the cell unit is not limited to this. A cell unit having a configuration in which the channels of each channel plate on the anode side are orthogonal to each other may be used.

[0060]

As is apparent from the above, the present invention has a cell structure in which a solid polymer film is interposed between a cathode and an anode, and this is sandwiched between two gas diffusion layers. An oxidant gas flows along the surface of the gas diffusion layer on the anode side, and a fuel gas flows along the surface of the gas diffusion layer on the anode side to generate electricity. The moisture permeability of the gas diffusion layer is lower than that of the gas diffusion layer on the cathode side in other areas, so that excessive moisture evaporation from the solid polymer membrane near the gas inlet on the cathode side Can be suppressed, and stable power generation can be performed.

[Brief description of the drawings]

FIG. 1 is an assembly diagram of a cell unit constituting a polymer electrolyte fuel cell according to a first embodiment.

FIG. 2 is a sectional view of a cell according to the first embodiment;

FIG. 3 is a sectional view of a cell according to a second embodiment.

FIG. 4 is a sectional view of a cell of variation 1.

FIG. 5 is a sectional view of a cell of variation 2.

FIG. 6 is a diagram showing experimental results of cells 1 to 6;

FIG. 7 is a view showing experimental results of cells 7-14.

[Explanation of symbols]

 Reference Signs List 10 cell unit 20 cell 21 solid polymer membrane 22 cathode (catalyst layer) 23 anode (catalyst layer) 24 cathode-side gas diffusion layer (current collector) 25 anode-side gas diffusion layer (current collector) 50 anode-side channel plate 60 Cathode side channel plate

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H018 AA06 AS02 AS03 EE18 HH00 HH03 HH05 5H026 AA06 CC03 EE19 HH00 HH03 HH05 5H027 AA06

Claims (9)

[Claims] 1. A cell structure in which a solid polymer film is interposed between a cathode and an anode and sandwiched between two gas diffusion layers, and an oxidant gas is formed along the surface of the gas diffusion layer on the cathode side. A polymer electrolyte fuel cell that generates power by allowing fuel gas to flow along the surface of the gas diffusion layer on the anode side, wherein the water permeability of the gas diffusion layer on the cathode side near the gas inlet is: A polymer electrolyte fuel cell, wherein the water permeability of the gas diffusion layer on the cathode side in other regions is lower than that of the gas diffusion layer. 2. The thickness of the gas diffusion layer on the cathode side is:
2. The polymer electrolyte fuel cell according to claim 1, wherein the amount increases along the direction from the vicinity of the gas outlet to the vicinity of the gas inlet. 3. The thickness of the gas diffusion layer on the cathode side is:
3. The structure according to claim 2, wherein the temperature increases linearly along the direction from the vicinity of the gas outlet to the vicinity of the gas inlet.
9. The polymer electrolyte fuel cell according to item 1. 4. The gas diffusion layer on the cathode side, wherein a ratio of a thickness near a gas inlet to a thickness near a gas outlet is in a range of 1.05 to 2.00. 9. The polymer electrolyte fuel cell according to item 1. 5. A structure in which the thickness of the cell is made constant by changing the thickness of at least one of the anode and the gas diffusion layer on the anode side in accordance with the thickness of the gas diffusion layer on the cathode side. The polymer electrolyte fuel cell according to any one of claims 2 to 4. 6. The structure according to claim 1, wherein the water repellent content of the gas diffusion layer on the cathode side increases along the direction from the vicinity of the gas outlet to the vicinity of the gas inlet. The polymer electrolyte fuel cell according to any one of the above. 7. The ratio of the water repellent content of the gas diffusion layer on the cathode side to the vicinity of the gas inlet to the vicinity of the gas outlet is in the range of 1.05 to 2.00. 9. The polymer electrolyte fuel cell according to item 1. 8. The content of a water repellent near the gas inlet of the gas diffusion layer on the cathode side is less than 15% of the gas diffusion layer.
The polymer electrolyte fuel cell according to claim 6, wherein the value is a value selected from a range of about 90 wt%. 9. The polymer electrolyte fuel cell according to claim 6, wherein the water repellent is a fluororesin.