JP2002164057A - Solid high molecular fuel cell and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid high molecular fuel cell and its manufacturing method, capable of preventing excess or insufficient water content in the catalyst, and the gas diffusion inhibition, with respect to the fuel cell using a catalyst layer containing an ion exchange resin. SOLUTION: In this solid high molecular fuel cell comprising the catalyst layers 11 formed on both main faces through a solid high molecular catalyst film, a gas diffusion layer 3 and a separator having a reaction gas channel, the catalyst layers include the catalyst powder and the ion exchange resin, and EW of the ion exchange resin in the catalyst layers is changed along the thickness direction and the face direction of the catalyst layers. Most preferably, EW in the thickness direction of the catalyst layers 11 is large at the gas diffusion layer 3 side and small at the solid high molecular electrolytic film side, and EW in the face direction is large at an outlet side of the reaction gas, and small at its inlet side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polymer electrolyte fuel cell and a method for manufacturing the same.

[0002]

2. Description of the Related Art A fuel cell is a device that generates direct current electricity using hydrogen and oxygen with an electrolyte interposed therebetween. The polymer electrolyte fuel cell uses a resin film that exhibits ionic conductivity when the polymer membrane contains water as an electrolyte. FIG. 8 is a perspective view of the structure of the fuel cell, and FIG. FIG. 7 is an enlarged sectional view.

[0003] In FIGS. 7 and 8, a catalyst layer 2 and a porous gas diffusion layer 3 are provided on both surfaces of a solid polymer electrolyte membrane 1.
And a fuel gas flow path for supplying / discharging a fuel gas containing hydrogen as a reaction gas to one gas diffusion layer, and supplying an oxidizing gas as a reaction gas to the other diffusion layer. And a separator 5 having an oxidizing gas flow path for discharging. In FIG. 8, the separator has a reaction gas flow path on both sides of one separator. However, for manufacturing reasons, a separator having a flow path on one side is stacked back to back as shown in FIG. In some cases. A stack of many of the above cells is called a stack.

As the solid polymer electrolyte membrane 1, a perfluorosulfonic acid polymer membrane (trade name, DuPont, USA)
Nafion membrane) is used. This membrane shows specific resistance of 20 Ω · cm or less at room temperature by being saturated with water, and functions as a proton conductive electrolyte. The saturated water content of the membrane changes reversibly with temperature.

By supplying hydrogen from one side of the gas diffusion layer 3 bonded to both sides of the solid polymer electrolyte membrane 1 and oxygen or air from the other side, the solid polymer electrolyte membrane 1
Oxidation of hydrogen and reduction of oxygen at the interface between the catalyst and the catalyst layer 2 cause the transfer of protons and electrons to generate electricity.

[0006] The catalyst layer 2 is formed of particulate platinum black or platinum-carrying carbon and a water-repellent fluororesin. As the catalyst layer 2, a catalyst with an electrolyte resin having a configuration in which an ion exchange resin, for example, a solid polymer electrolyte resin is mixed in the catalyst layer, is often used in order to increase the reaction area of the catalyst.

As the gas diffusion layer 3, conductive carbon paper or carbon cloth is used. Normally, after forming a joined body of the solid polymer electrolyte membrane 1 and the catalyst layer 2, the gas diffusion layer 3 is joined by hot pressing. First, the catalyst layer 2 is applied on the gas diffusion layer 3 and joined. After that, a joined body with the solid polymer electrolyte membrane 1 may be produced.

As described above, since the solid polymer electrolyte membrane used in the solid polymer electrolyte fuel cell exhibits high ionic (proton) conductivity in a wet state containing water, the reaction gas is water. High battery characteristics can be obtained by humidification.

Since the gas near the outlet of the reaction gas inside the unit cell contains a large amount of water (steam) generated by the upstream reaction, it is relatively difficult to keep the solid polymer electrolyte membrane in a wet state. Easy. On the other hand, in the vicinity of the inlet of the reaction gas, in particular, the amount of water (steam) taken away by the flowing reaction gas becomes larger than the water produced by the reaction, and the solid polymer electrolyte membrane is dried to cause a partial deterioration in characteristics.

As a method of humidifying the reaction gas, a method of humidifying the reaction gas in a humidification tank or the like provided outside the stack and then supplying the humidified gas (external humidification method), or a method of humidifying the same size / shape as the unit cell is used. Incorporate cells as part of the stack,
A method (internal humidification method) of supplying a reaction gas passing through a humidification cell to a power generation unit has been considered.

For example, as an external humidification system, a reaction gas is diffused in water stored in a humidification container, and the reaction gas degassed from the water is passed to the laminated fuel cell. In addition, as the internal humidification method, a separator having a gas circulation groove, and a separator having a humidification water circulation groove sandwich a water permeable membrane via a porous support, and constitute a humidification plate as a whole, as a humidification film And the like, in which the reaction gas is humidified via the water permeable membrane.

[0012]

As described above, in order to operate the fuel cell stably in the polymer electrolyte fuel cell, it is necessary to always keep an appropriate amount of water in the electrolyte. In general, the operating temperature of a polymer electrolyte fuel cell is often around 70 ° C., and since water can exist in both a water vapor and a liquid form in the cell, the utilization rate of the reaction gas is not less than a certain level. , The water vapor concentration changes considerably along the flow path of the reaction gas.

When humidification is performed so that sufficient water can be supplied to the electrolyte on the upstream side of the reaction gas, the steam becomes excessive on the downstream side. Conversely, if the amount of humidification is reduced so that the supply of moisture is sufficient on the downstream side to prevent dew condensation, moisture is insufficient on the upstream side and the ionic conductivity of the electrolyte decreases.

As described above, in the conventional humidification method for the polymer electrolyte fuel cell, it is difficult to obtain an appropriate humidified state over the entire electrolyte, and there has been a problem that the output characteristics of the fuel cell deteriorate. When the fuel cell is operated continuously for a long period of time, the generated water accumulates and gas diffusion is hindered, and the output characteristics of the fuel cell are further reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and it is an object of the present invention to provide a fuel cell including an ion exchange resin in a catalyst layer, in which excess or deficiency of water in an electrolyte and occurrence of gas diffusion inhibition occur. It is an object of the present invention to provide a polymer electrolyte fuel cell and a method of manufacturing the same, which are prevented.

[0016]

In order to solve the above-mentioned problems, the present invention provides a catalyst layer disposed on both main surfaces with a solid polymer electrolyte membrane interposed therebetween, and a catalyst layer disposed on both outer sides of the catalyst layer. A porous gas diffusion layer, a first separator having a fuel gas flow path for supplying and discharging a fuel gas containing hydrogen to one of the gas diffusion layers, and an oxidizing agent for the other gas diffusion layer. In a polymer electrolyte fuel cell comprising a second separator having an oxidizing gas flow path for supplying and discharging gas, the catalyst layer comprises catalyst powder and EW (equivalent weight of ion exchange groups). ), And the EW of the ion exchange resin in the catalyst layer is changed along the thickness direction and the surface direction of the catalyst layer (claim). Item 1)).

In the fuel cell according to the first aspect of the present invention, the EW in the thickness direction of the catalyst layer is set to be large on the gas diffusion layer side and small on the solid polymer electrolyte membrane side. In addition, the EW in the plane direction is set large at the outlet side of at least one of the fuel gas and the oxidizing gas and small at the inlet side (the invention of claim 2).

As the ion exchange resin, the same resin as the solid polymer electrolyte, for example, the perfluorosulfonic acid polymer can be used.

Here, the EW indicates an equivalent weight of an exchange group having proton conductivity, and is a dry weight of the ion exchange membrane per equivalent of the ion exchange group. Expressed in units. Since the ion exchange resin having a smaller EW has a relatively higher hydrophilicity, it is possible to cause a difference in the water content according to the magnitude of the EW.

Therefore, according to the configuration of the present invention, the gas diffusion property of the catalyst layer on the gas diffusion layer side is kept good, and the gas diffusion inhibition on the gas outlet side where the water produced by the reaction of the fuel cell becomes excessive is good. Can be prevented.

The method for manufacturing the fuel cell includes the following:
The inventions of claims 3 and 4 are preferable. That is, a step of preparing a plurality of types of slurries in which a catalyst, an ion exchange resin, and a volatile organic solvent are mixed by changing the EW of the ion exchange resins, and converting the plurality of types of slurries from conductive carbon paper or carbon cloth. Forming a catalyst layer on the gas diffusion layer or the solid polymer electrolyte membrane such that the EW of the ion exchange resin in the catalyst layer changes along the thickness direction and / or the plane direction of the catalyst layer; (The invention of claim 3).

Further, in the manufacturing method according to claim 3, the EW in the thickness direction of the catalyst layer is set to be large on the gas diffusion layer side, small on the solid polymer electrolyte membrane side, and / or The EW in the direction is made larger at the outlet side of at least one of the fuel gas and the oxidizing gas and smaller at the inlet side (the invention of claim 4).

According to the above manufacturing method, a plurality of desired EWs
The catalyst layer having in advance is prepared, and applied on the gas diffusion layer or the electrolyte membrane to form the catalyst layer in order, so that the catalyst layer may be formed in an arbitrary portion regardless of the thickness direction of the catalyst layer or the surface direction. The EW can be adjusted. Therefore, the EW of the ion exchange resin should be
Thus, a desired catalyst layer can be easily formed.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

(Example 1) FIG. 1 is a view showing a flow of manufacturing a catalyst layer according to an example of the present invention. As the ion exchange resin in the catalyst layer of this embodiment, a perfluorosulfonic acid polymer was used, and the EW on the upstream side of the reaction gas was 90%.
0, EW on the downstream side is 1100, and E in the surface direction of the catalyst layer is
Only W was changed.

Referring to FIG. 1, the procedure for preparing the catalyst layer of this embodiment will be described below. Pure water is added to the carbon particles at a ratio of about 3 ml with respect to 1 g of the catalyst supporting the platinum fine particles, followed by stirring and dispersion. Furthermore, ion exchange resin (EW
= 900) in a ratio of about 7 ml to 1 g of the catalyst, followed by stirring and dispersion.

The slurry thus obtained is applied directly on the upstream side of the electrolyte membrane by a coating method or a transfer method. Subsequently, in the same manner, the downstream side is formed by coating instead of the ion exchange resin (EW = 1100).

The fuel cell manufactured as described above was operated under predetermined operating conditions, and a comparative experiment was performed with a fuel cell manufactured by a conventional method. FIG. 2 shows the result. In FIG. 2, the vertical axis indicates the cell voltage (mV), the horizontal axis indicates the operation time, and the curve A of the change over time indicates the fuel cell of this example. Curves B and C are fuel cells according to the conventional method without changing the EW in the surface direction of the catalyst layer,
The EW for curves B and C are 900 and 11 respectively.
00 is shown.

As operating conditions, an operating temperature of 80
℃, 72 ° C saturated humidification of cathode, air utilization rate 60%,
The current density was 400 mA / cm ² .

According to FIG. 2, the fuel cell A manufactured according to the present embodiment has a high initial characteristic and a small rate of voltage decrease due to long-term operation. On the other hand, both of the fuel cells B and C manufactured by the conventional method have lower initial characteristics than those of the present embodiment, and have a large reduction rate.

(Embodiment 2) FIG. 3 is a flow chart of the preparation of the catalyst layer according to Embodiment 2, FIG. 4 is a partial cross-sectional view of the catalyst layer and the electrolyte membrane, and FIG. Similar experimental results are shown.

In Example 2, E was measured in the plane direction of the catalyst layer.
The point that EW in the thickness direction of the catalyst layer was changed together with W was changed, and other manufacturing conditions and operating conditions were the same as in Example 1.

As shown in FIG. 4, in the second embodiment,
E of the ion exchange resin in the catalyst layer 2a on the electrolyte membrane 1 side
W was 900, the EW of the ion exchange resin in the catalyst layer 2b on the gas diffusion layer side (not shown) upstream of the reaction gas was 1000, and the EW of the ion exchange resin in the catalyst layer 2c on the downstream side was 1100.

The flow of preparing the catalyst layer in FIG. 3 is the same as that in FIG. 1 except that it has three stages according to the above three types of EW, and therefore the description is omitted.

In FIG. 5, the curve AA of the change over time shows the case of the second embodiment, and the curve A is the curve AA of the first embodiment.
Is the same as The fuel cell manufactured according to the second embodiment has improved initial characteristics as compared with the fuel cell manufactured according to the first embodiment, but the voltage reduction rate is almost the same as that of the first embodiment.

Embodiment 3 FIG. 6 shows an example of a catalyst layer formed on a gas diffusion layer. In FIG. 6, the catalyst layer 11 formed on the gas diffusion layer 3 is divided into two parts in the thickness direction of the catalyst layer and two parts in the plane direction, and a slurry in which the EW of the ion exchange resin is changed is applied and laminated. It is formed. The EW in the thickness direction of the catalyst layer of the catalyst layer 11 is large on the gas diffusion layer side and small on the solid polymer electrolyte membrane side, and the EW in the plane direction of the catalyst layer is large on the exit side of the reaction gas. Make the entrance side small. According to the above, a more preferable catalyst layer can be obtained as compared with Examples 1 and 2.

[0037]

As described above, according to the present invention, a catalyst layer disposed on both main surfaces with a solid polymer electrolyte membrane interposed therebetween, and a porous gas diffusion layer disposed on both outer sides of the catalyst layer And a first separator having a fuel gas flow path for supplying and discharging a fuel gas containing hydrogen to one of the gas diffusion layers,
In a polymer electrolyte fuel cell comprising: a second separator having an oxidizing gas flow path for supplying and discharging an oxidizing gas to the other gas diffusion layer, the catalyst layer includes a catalyst powder and It is configured to include at least two types of ion exchange resins having different EW (equivalent weight of ion exchange groups), and the EW of the ion exchange resin in the catalyst layer is changed along the thickness direction and the surface direction of the catalyst layer. In the most preferred embodiment, the EW in the thickness direction of the catalyst layer is large on the gas diffusion layer side, small on the solid polymer electrolyte membrane side, and the EW in the plane direction is small. By making the outlet side of at least one of the fuel gas and the oxidizing gas large and the inlet side small, the gas diffusion property of the catalyst layer on the gas diffusion layer side is kept good, and the water generated by the reaction water of the fuel cell is used. Be too much The gas diffusion inhibition of the scan outlet side can be effectively prevented.

Further, as a method of manufacturing the fuel cell, a plurality of types of slurries in which a catalyst, an ion exchange resin and a volatile organic solvent are mixed are prepared by changing the EW of the ion exchange resin. The slurry is placed on a gas diffusion layer made of conductive carbon paper or carbon cloth or on a solid polymer electrolyte membrane, and the EW of the ion exchange resin in the catalyst layer is applied along the thickness direction and / or the plane direction of the catalyst layer. And the step of coating and forming as a catalyst layer so as to change, the thickness direction of the catalyst layer,
Regardless of the plane direction, it is easy to adjust the EW in the catalyst layer in any part, and furthermore, to adjust the gas diffusivity, so that a desired catalyst layer can be easily formed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a production flow of a catalyst layer according to Embodiment 1 of the present invention.

FIG. 2 is a diagram showing output characteristics of a fuel cell according to Example 1 in comparison with a conventional method.

FIG. 3 is a diagram showing a production flow of a catalyst layer according to Embodiment 2 of the present invention.

FIG. 4 is a partial cross-sectional view of a catalyst layer and an electrolyte layer according to Example 2.

FIG. 5 is a diagram showing output characteristics of the fuel cell according to the second embodiment in comparison with the first embodiment.

FIG. 6 is a partial cross-sectional view of a catalyst layer and a gas diffusion layer according to Example 3.

FIG. 7 is a perspective view of a configuration of a polymer electrolyte fuel cell.

FIG. 8 is a partially enlarged cross-sectional view of a polymer electrolyte fuel cell.

[Explanation of symbols]

1: solid polymer electrolyte membrane, 2, 2a, 2b, 2c, 1
1: catalyst layer, 3: gas diffusion layer, 5: separator.

Claims (4)

[Claims] 1. A catalyst layer provided on both main surfaces with a solid polymer electrolyte membrane interposed therebetween, a porous gas diffusion layer provided on both outer sides of the catalyst layer, and hydrogen gas supplied to one of the gas diffusion layers. A first separator having a fuel gas flow path for supplying and discharging a fuel gas containing the oxidizing gas flow path for supplying and discharging an oxidizing gas to the other gas diffusion layer; Wherein the catalyst layer comprises a catalyst powder and at least two types of ion exchange resins having different EWs (equivalent weights of ion exchange groups). A polymer electrolyte fuel cell characterized in that the EW of the ion exchange resin in the catalyst layer is changed along the thickness direction and the surface direction of the catalyst layer. 2. The fuel cell according to claim 1, wherein the EW in the thickness direction of the catalyst layer is large on the gas diffusion layer side, small on the solid polymer electrolyte membrane side, and EW in the plane direction.
Wherein at least one of the outlet side of the fuel gas or the oxidizing gas is large and the inlet side is small. 3. A step of preparing a plurality of types of slurries in which a catalyst, an ion exchange resin and a volatile organic solvent are mixed by changing the EW of the ion exchange resins, and converting the plurality of types of slurries into conductive carbon paper or Formed as a catalyst layer on a gas diffusion layer composed of carbon cloth or a solid polymer electrolyte membrane such that the EW of the ion exchange resin in the catalyst layer changes along the thickness direction and / or the plane direction of the catalyst layer. A method of manufacturing a polymer electrolyte fuel cell. 4. The production method according to claim 3, wherein the EW in the thickness direction of the catalyst layer is large on the gas diffusion layer side, small on the solid polymer electrolyte membrane side, and / or in the plane direction. The method of manufacturing a polymer electrolyte fuel cell, wherein the EW of at least one of the fuel gas and the oxidant gas is large and the EW is small at the inlet side.