JPH10154521A - Polymer electrolyte fuel cell - Google Patents

Abstract

(57) [Problem] To realize a polymer electrolyte fuel cell that operates without humidification without using an ion exchange membrane having a thin film thickness without damaging the ion exchange membrane and reducing the hydrogen utilization rate. . SOLUTION: When the thickness of the ion exchange membrane is 50 μm or less,
By using an electrode in which the area of the catalyst layer is smaller than that of the diffusion layer and an ion exchange membrane having a reinforcing film provided on at least one side with a window frame of the same shape as the catalyst layer, the ion exchange membrane operates without humidification. Thus, a polymer electrolyte fuel cell free from damage can be obtained.

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 ion exchange membrane for a polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art Polymer electrolyte fuel cells (hereinafter referred to as PEFCs).
Is an ion exchange membrane which is a solid polymer electrolyte, and a noble metal catalyst is used as an electrode catalyst.

When hydrogen is used as fuel in PEFC, the reaction of Chemical Formula 1 occurs at the negative electrode.

[0004]

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When oxygen is used as the oxidizing agent, the reaction of the chemical formula (2) occurs at the positive electrode, and water is generated.

[0006]

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The ion exchange membrane does not exhibit ionic conductivity unless the moisture content exceeds a certain level.
Reaction does not occur. In addition, even if it shows ionic conductivity, if the water content is low, the resistance of the ion exchange membrane increases, and the output decreases due to IR loss. Therefore, in the PEFC, the fuel gas and the oxidizing gas are humidified and supplied in order to sufficiently contain the ion exchange membrane. The water used for humidification must be pure water having a conductivity of 10 ^-2 Scm or less without containing impurities such as organic substances, chlorine ions, and metal ions in order to prevent contamination of the membrane and the catalyst. Since the humidification water is consumed together with the operation of the PEFC, it needs to be replenished. In order to eliminate the supply of pure water, there is a system for circulating the reaction gas to recover water (U.S. Pat. No. 5,200,278). However, in order to prevent contamination of impurities, a filter of ion exchange resin is provided. The system becomes complicated.

[0008] For the application of PEFC to small consumer power sources,
It is desirable that the reaction gas be non-humidified in order to make the system simpler. However, simply dehumidifying the reaction gas does not sufficiently humidify the ion-exchange membrane, increases the resistance, and degrades the characteristics. In order to solve this problem, a noble metal and metal oxide fine particles are contained in the ion exchange membrane, and hydrogen and oxygen that cross over are directly reacted in the ion exchange membrane to humidify the ion exchange membrane with water ( JP-A-7-
No. 90111). At this time, the thickness of the ion exchange membrane is 3
The thickness is 0 to 200 μm, preferably 50 to 100 μm.

However, when the thickness of the ion exchange membrane is 50
When the thickness is reduced to about μm, crossover occurs in which the reaction gas passes through the ion exchange membrane, and the voltage is reduced. FIG. 3 is a cross-sectional view of a conventional polymer electrolyte fuel cell. Electrodes 4 each comprising a catalyst layer 2 and a diffusion tank 3 are arranged on both sides of the ion exchange membrane 1, and a gasket 5 is arranged on the outer periphery of the electrodes 4, and these are sandwiched by a separator 6 to constitute a unit cell. Nothing supports the ion exchange membrane 1 between the electrode 4 and the gasket 5. Therefore, if the thickness of the ion exchange membrane is small, the following problems occur. During the assembly of the battery, mechanical stress was applied to the ion exchange membrane, and the ion exchange membrane was sometimes damaged. In addition, during operation, the ion exchange membrane around the electrode expands and contracts due to a change in the moisture content of the membrane-electrode assembly and drying. Due to this dimensional change, the ion exchange membrane was stressed and sometimes damaged. Further, the ion exchange membrane may be broken by the pressure difference between the fuel gas and the oxidizing gas. When the electrode and the ion exchange membrane are joined by hot pressing, the ion exchange membrane may be damaged at the edge of the diffusion layer of the electrode. As described above, when the ion exchange membrane is broken, a serious problem arises in safety such as fuel gas and oxidizing gas being mixed and burning on the catalyst.

Therefore, the following improvements have been made to prevent the breakage of the film. A gas-impermeable reinforcing membrane is disposed so as to cover the periphery of the electrode and the outer edge of the ion-exchange membrane where the electrode is not disposed, and to overlap the gas-sealed portion (Japanese Patent Laid-Open No. 5-242897). A liquid or sheet-like sealing material is used together with the sealing material so as to overlap around the surface of the electrode of the electrode assembly (Japanese Patent Application Laid-Open No. 8-45517), and a flat reinforcing member is attached to the membrane-electrode assembly. Joining using a sealant (Japanese Patent Laid-Open No. 7-65)
No. 847), a frame-shaped sheet protective film which is in close contact with the periphery of the ion exchange membrane and overlaps the electrodes is provided on at least one side of the ion exchange membrane (Japanese Patent Laid-Open No. 5-21).
No. 077, 5-174845) and an ion exchange membrane having a small ion exchange capacity (hereinafter referred to as EW). W. Using an ion-exchange membrane integrated with an ion-exchange membrane sandwiched between large-sized ion-exchange membranes (JP-A-6-251780), forming an auxiliary gasket with a sealing material around the periphery of a diffusion layer (JP-A-7-220742), and the like. This is the method.

[0011]

However, when an ion-exchange membrane having a small thickness is used, the above-mentioned Japanese Patent Application Laid-Open No. 5-24 / 1993 has been proposed.
In the configurations of JP-A-2897, JP-A-8-45517 and JP-A-7-65847, in order to reinforce the membrane-electrode assembly, damage of the membrane due to the edge of the diffusion layer when joining the electrode and the membrane is prevented. There was a disadvantage that it could not be prevented. Further, in the configurations of JP-A-5-242897 and JP-A-8-45517, since the protective film or the seal portion overlaps with the electrode, the area where the reaction gas is supplied is smaller than the electrode area. . FIG. 4
JP-A-5-21077 and JP-A-5-17-1
In the configuration disclosed in Japanese Patent No. 74845, since the electrode 4 is bonded to the ion exchange membrane 1 having the reinforcing membrane 7, breakage of the ion exchange membrane 1 at the time of bonding can be prevented. However, since the reinforcing membrane 7 exists between the electrode catalyst layer 2 and the ion exchange membrane 1, there is a disadvantage that the effective area of the electrode 4 and the ion exchange membrane 1 is reduced. Further, in the configuration of JP-A-6-251780, there is a waste that an expensive ion-exchange membrane is bonded to a portion not requiring ionic conductivity, and in the configuration of JP-A-7-220742, the coating process of the sealing material is complicated. It is.

Further, the above-described conventional configuration for the non-humidifying operation has a disadvantage that hydrogen is consumed by a chemical reaction and the utilization rate of hydrogen is reduced.

The present invention solves such a conventional problem, and provides a polymer electrolyte fuel cell in which even if a thin film is used, the ion exchange membrane is prevented from being damaged and the sealing property is improved. The purpose is to do so. Another object of the present invention is to provide a polymer electrolyte fuel cell that operates without humidification without lowering the hydrogen utilization rate.

[0014]

In order to solve the above-mentioned problems, a polymer electrolyte fuel cell according to the present invention uses an ion exchange membrane having a thickness of 50 μm or less, and a gas diffusion electrode having an area of a catalyst layer. Is smaller than the area of the diffusion layer, and the peripheral portion of the catalyst layer is inside the peripheral portion of the diffusion layer, and the ion-exchange membrane has at least one surface of a frame-shaped protective film with a window corresponding to the shape of the catalyst layer. Side.

According to the above configuration, even when an ion exchange membrane as thin as 50 μm or less is used, breakage of the ion exchange membrane can be prevented without reducing the effective area between the electrode and the ion exchange membrane, and The membrane can be prevented from being damaged at the time of assembling and operating the battery, and the sealing property can be improved.

Further, the polymer electrolyte fuel cell according to the present invention comprises:
The oxidant gas is supplied to the positive electrode and the fuel gas is supplied to the negative electrode without humidification.

With the above structure, the concentration gradient of water in the membrane electrode assembly is increased, and the diffusion of water generated at the positive electrode to the negative electrode side (reverse diffusion) is apt to occur, so that the ion exchange membrane is easily humidified. Since the absolute amount of water for humidifying the ion-exchange membrane is reduced, the ion-exchange membrane can be sufficiently humidified with only the produced water. For this reason, the non-humidifying operation can be performed without including the noble metal fine particles and the metal oxide fine particles in the ion exchange membrane.

[0018]

DETAILED DESCRIPTION OF THE INVENTION A polymer electrolyte fuel cell according to the present invention comprises a gas diffusion electrode comprising an ion exchange membrane and a catalyst layer and a diffusion layer provided on both sides of the ion exchange membrane. In the above, the peripheral portion of the catalyst layer is inside the peripheral portion of the diffusion layer, and the ion-exchange membrane has a thickness of 50 μm or less, and at least one of the frame-shaped reinforcing films having a window corresponding to the shape of the catalyst layer is opened. It is a polymer electrolyte fuel cell having a surface side.

FIG. 1 is a sectional structural view of a polymer electrolyte fuel cell according to one embodiment of the present invention. As shown in FIG.
Is smaller than the area of the diffusion layer 3 and the peripheral edge of the catalyst layer 2 is inside the peripheral edge of the diffusion layer 3.
Exchange membrane 1 having a frame-shaped reinforcing membrane 7 provided with a window frame conforming to the shape of the catalyst layer 2 on at least one surface side
Consists of 5 is a gasket, 7 is a separator.

With such a configuration, the reinforcing membrane 7 and the electrode catalyst layer 2 do not overlap, so that the contact area between the electrode 4 and the ion exchange membrane 1 does not decrease, and the edge of the electrode diffusion layer 3 The portion can be located at the portion where the reinforcing film 7 exists. Therefore, even when a thin ion exchange membrane having a thickness of 50 μm or less is used, breakage of the membrane at the time of joining the membrane and the electrode, assembling and operating the battery can be prevented, and the sealing property can be improved.

Further, the present invention is a polymer electrolyte fuel cell in which an oxidizing gas is supplied to a positive electrode and a fuel gas is supplied to a negative electrode without humidification.

In a polymer electrolyte fuel cell, the smaller the ion exchange membrane is, the lower the internal resistance is and the more excellent the cell characteristics are. Furthermore, by adopting such a configuration, the absolute amount of water for humidifying the ion exchange membrane becomes small, and the concentration gradient of water becomes large, so that reverse diffusion of generated water becomes easy, and only the generated water is used. The ion exchange membrane can be sufficiently humidified. Therefore, this solid polymer electrolyte fuel cell can be operated without humidification.

In the embodiment of the present invention shown in FIG. 1, the shape of the catalyst layer and the window frame of the protective film are the same, but the window frame may be substantially the same as the shape of the catalyst layer. Shall not overlap with Further, even if there is a gap between the catalyst layer and the window frame of the protective film before assembly, it is possible to match the gap by tightening each component at the time of assembling the battery.

In one embodiment of the present invention shown in FIG. 1, the reinforcing membrane is provided on one side of the ion exchange membrane. However, as shown in FIG. 2, the reinforcing membrane is provided on both sides of the ion exchange membrane. The same effect can be obtained for the case.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 An alcohol solution of a solid polymer electrolyte and an organic solvent were mixed and stirred, and a colloidal dispersion of the solid polymer electrolyte was mixed with a carbon powder catalyst supporting a platinum catalyst to form a paste. And coated on carbon paper that has been water-repellent with a fluororesin to form a catalyst layer (50 m
m × 50 mm) and a diffusion layer (55 mm × 55 mm) to form positive and negative gas diffusion electrodes. The platinum catalyst amount was 0.5 mg / cm ² for both the positive and negative electrodes. The mass of the polymer electrolyte was 1.0 mg / cm ² for both the positive and negative electrodes, and the reinforcing membrane (8) was provided with a 50 mm × 50 mm window frame having the same shape as the catalyst layer.
Ion exchange membrane (80 mm x 8) with 0 mm x 80 mm
0 mm). The electrode and the ion exchange membrane are 12
It was hot-pressed at 0 to 150 ° C. and 20 to 200 kgf / cm ² to produce a membrane electrode assembly. The ion exchange membrane used was Nafion 112 (50 μm in film thickness) manufactured by DuPont, USA. The reinforcing membrane was a sheet with a 50 μm-thick fluororesin adhesive provided with a window frame having the same shape as the catalyst layer, and was attached to one side of the ion exchange membrane. Fig. 1
Cell A of a polymer electrolyte fuel cell provided with the reinforcing membrane shown in (1) was prepared.

Comparative Example 1 A gas diffusion electrode comprising a catalyst layer and a diffusion layer of the same size of 50 mm × 50 mm was prepared.
Ion exchange membrane without a reinforcing membrane (80 mm x 80 mm)
The procedure was the same as in Example 1 except for using, and a unit cell B without a reinforcing film shown in FIG. 3 was produced.

(Comparative Example 2) A unit cell C was prepared in the same manner as in Example 1 except that Nafion 115 (130 µm in thickness) manufactured by DuPont, USA was used for the ion exchange membrane.

(Comparative Example 3) The window frame of the reinforcing film was set to 45 mm × 4 so that the inner periphery of the reinforcing film overlapped the peripheral portion of the catalyst layer by about 5 mm.
A unit cell D shown in FIG. 4 was produced in the same manner as in Example 1 except that the unit cell was provided at 5 mm.

Example 2 The ion exchange membrane used in Example 1 was replaced with Nafion 112 (50 μm in film thickness) manufactured by DuPont, USA, and G was manufactured by Japan Gore-Tex Corporation.
ORE-SELECT (film thickness of 20 μm and 10 μm
Single cells E and F were prepared in the same manner as in Example 1 except that m) was used.

(Comparative Example 4) The ion exchange membrane used in Comparative Example 1 was replaced by Nafion 112 (50 μm in film thickness) manufactured by DuPont USA, and G was manufactured by Japan Gore-Tex Corporation.
ORE-SELECT (film thickness of 20 μm and 10 μm
Cell batteries G and H were prepared in the same manner as in Comparative Example 1 except that m) was used.

The discharge tests in the non-humidifying operation and the humidifying operation were performed by supplying hydrogen gas to the negative electrode side and air to the positive electrode side of the unit cells A to H of the examples and comparative examples of the present invention. In the non-humidifying operation, both the hydrogen gas and the air were supplied without humidification and without heating, and the cells were not heated. In the humidifying operation, the hydrogen gas was supplied at 60 ° C. and the air was supplied at 40 ° C., and the operating temperature was 50 ° C.

Table 1 shows the number of damaged ion exchange membranes in the cells A, E and F of the example of the present invention and the cells B, D and H of the comparative example.

[0034]

[Table 1]

When air and hydrogen were supplied, and no heat was generated in the unloaded unit cell, it was determined that the ion exchange membrane was damaged. In the case of using the 50 μm ion exchange membrane, in the cell B without the reinforcing membrane, the ion exchange membrane was damaged in 2 out of 10 cells. However, the cells A and D using the reinforcing membrane were used.
Did not show any damage to the ion exchange membrane. 20μ
In the case of using the ion exchange membrane of m, the ion exchange membrane was damaged in 6 out of 10 cells in the unit cell G without the reinforcing membrane, but the ion exchange membrane was observed in the unit cell E using the reinforcing membrane. No damage was seen. Furthermore, when the ion exchange membrane of 10 μm is used, the cell H without the reinforcing membrane has a capacity of 10 μm.
Although the ion exchange membrane was damaged in all the cells, the ion exchange membrane was not damaged in the single cell F using the reinforcing membrane. From these results, when the reinforcing membrane was used, no breakage occurred even if the thickness of the ion exchange membrane was 50 μm or less.

FIG. 5 shows the current-voltage curves of the cells A, E and F of the example of the present invention and the cells C of the comparative example during the non-humidifying operation and the humidifying operation. In addition, the cell voltage of the non-humidifying operation of all the cells was lower than that at the time of the humidifying operation. However, while the voltage drop in the cells A, E and F is as small as several tens of mV, the voltage difference is large in the cell C having a film thickness of 130 μm, especially at a current density lower than 0.2 A / cm ^2. Markedly reduced.

FIG. 6 shows the relationship between the current value and the internal resistance in the non-humidifying operation and the humidifying operation of the unit cells A, E and F of the embodiment of the present invention and the unit cell C of the comparative example. Further, in all the cells, the internal resistance in the non-humidifying operation increased as compared with that in the humidifying operation, but the internal resistance of the cell C having a large film thickness as compared with the cells A, E and F increased remarkably. .

In the case of the non-humidifying operation, the ion exchange membrane is humidified only by the generated water. The smaller the film thickness, the smaller the amount of water required to humidify the ion exchange membrane may be smaller, and the smaller the film thickness, the higher the moisture content of the ion exchange membrane and the lower the resistance if the same moisture amount is used. . In addition, when the film thickness is small, the concentration gradient of water becomes large, the water generated at the positive electrode is easily diffused, and the ion exchange membrane is easily humidified. The thickness of the ion exchange membrane used for the cell A of the present example is as thin as 50 μm. Therefore, it can be said that the cell A has a relatively high water content of the ion exchange membrane and a low internal resistance even in the non-humidifying operation, and has a polarization characteristic comparable to that of the humidifying operation. It is considered that these effects are increased in the cells E and F using the ion-exchange membranes with a smaller thickness, the operation without humidification is facilitated, and the characteristics are higher than those of the cell A. On the other hand, cell C
Since the thickness of the ion-exchange membrane is as thick as 130 μm, the humidification of the ion-exchange membrane alone is insufficient due to the generated water alone, and the internal resistance becomes high. It is considered that the characteristics were deteriorated as compared with the humidification operation.

FIG. 7 shows a current-voltage curve in the non-humidifying operation of the unit cell A of the embodiment of the present invention and the unit cells B and D of the comparative example. The open circuit voltage of each of the cells A, B and D is 10
The values were 15 mV, 900 mV, and 1010 mV, and the cells A and D showed higher values than the cell B. In addition, the cells A and B had substantially the same polarization characteristics and exhibited characteristics superior to those of the cell D.

Since the cells A and D exhibited an open circuit voltage higher than that of the cell B, it can be said that the crossover of the reaction gas from the periphery of the electrode was suppressed by the reinforcing film. In the unit cell D, the area of the electrode and the ion exchange membrane is reduced because the reinforcing membrane overlaps with the electrode catalyst layer. However, it can be said that the cell A exhibited polarization characteristics superior to that of the cell D because the ion exchange membrane was reinforced without reducing the electrode area because the reinforcing membrane did not overlap the electrode catalyst layer.

In this example, a Nafion membrane manufactured by DuPont USA and GORE-SELECT manufactured by Japan Gore-Tex Co., Ltd. were used as the ion exchange membrane.
It is not limited to this as long as it is an ion exchange membrane exhibiting cation conductivity.

Although the fluororesin sheet is used for the reinforcing film, the same effect can be obtained as long as it has heat resistance and acid resistance. Although a sheet having an adhesive is used in this embodiment, the same effect can be obtained by integrating a sheet having no adhesive with an ion exchange membrane by heat fusion or the like. Further, in the present embodiment, a reinforcing membrane having a thickness of 50 μm was used, but the thickness of the reinforcing membrane is not limited to the thickness in the embodiment, but needs to be optimized according to the thickness of the ion exchange membrane.

Further, in this embodiment, the peripheral edge of the reinforcing membrane coincides with the peripheral edge of the ion exchange membrane. However, the same effect can be obtained if the peripheral edge of the reinforcing membrane is located outside the peripheral edge of the gas diffusion layer. Can be

[0044]

As described above, according to the present invention, even when a thin ion-exchange membrane is used, the ion-exchange membrane can be used during membrane electrode bonding, battery assembly and operation without reducing the reaction area of the electrodes. The present invention can prevent a breakage and can realize a polymer electrolyte fuel cell having excellent sealing properties.

In addition, it is possible to perform a non-humidifying operation of the polymer electrolyte fuel cell without reducing the hydrogen utilization rate by reacting hydrogen and oxygen in the ion exchange membrane.

[Brief description of the drawings]

FIG. 1 is a structural diagram showing a configuration of a polymer electrolyte fuel cell according to one embodiment of the present invention.

FIG. 2 is a structural view showing a configuration of a polymer electrolyte fuel cell according to another embodiment of the present invention.

FIG. 3 is a structural diagram showing a configuration of a polymer electrolyte fuel cell in a conventional example.

FIG. 4 is a structural view showing a configuration of a conventional polymer electrolyte fuel cell.

FIG. 5 is a diagram showing current-voltage characteristics of the polymer electrolyte fuel cells of Examples and Comparative Examples of the present invention.

FIG. 6 is a diagram showing the relationship between the current and the internal resistance of the polymer electrolyte fuel cells of Examples and Comparative Examples of the present invention.

FIG. 7 is a diagram showing current-voltage characteristics of the polymer electrolyte fuel cells of Examples and Comparative Examples of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ion exchange membrane 2 Catalyst layer 3 Diffusion layer 4 Gas diffusion electrode 5 Gasket 6 Separator 7 Reinforcement membrane

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Nobuo Eda 1006 Kazuma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. In a polymer electrolyte fuel cell comprising an ion exchange membrane and a gas diffusion electrode comprising a catalyst layer and a diffusion layer provided on both surfaces of the ion exchange membrane, the periphery of the catalyst layer is the periphery of the diffusion layer. And the ion exchange membrane has a thickness of 5
A polymer electrolyte fuel cell having a frame-shaped reinforcing membrane having a window having an opening corresponding to the shape of the catalyst layer on at least one side and having an ion exchange membrane of 0 μm or less. 2. The polymer electrolyte fuel cell according to claim 1, wherein an oxidizing gas is supplied to the positive electrode and a fuel gas is supplied to the negative electrode without humidification.