JP3416578B2 - Solid polymer electrolyte fuel cell - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a solid polymer electrolyte membrane interposed between a fuel electrode and an oxidant electrode to supply a fuel gas to the fuel electrode and an oxidant gas to the oxidant electrode. Then, the present invention relates to a solid polymer electrolyte fuel cell for generating electric power.

[0002]

2. Description of the Related Art In recent years, fuel cells, which have high energy conversion efficiency and do not generate harmful substances due to power generation reaction, have been attracting attention. Molecular electrolyte fuel cells are known.

FIG. 16 shows the power generation principle of a solid polymer electrolyte fuel cell, in which a fuel electrode (55) and an oxidizer electrode () are provided on both sides of an ion conductive solid polymer electrolyte membrane (54). 56)
And a fuel chamber (57) and an oxidant chamber (58) on both sides thereof to form a cell (50), and the fuel electrode (55) and the oxidant electrode (56) are connected to an external circuit. They are connected to each other via (59).

In the fuel electrode (55), hydrogen H ₂ contained in the fuel gas supplied to the fuel chamber (57) is decomposed into hydrogen ions H ⁺ and electrons e ⁻ , and the hydrogen ions H ⁺ are solid polymer. While moving inside the electrolyte membrane (54) toward the oxidant electrode (56) in a form hydrated with water molecules in the electrolyte membrane (54), the electron e ⁻ moves through the external circuit (59) to the oxidant electrode (56). Flow toward 56). In the oxidant electrode (56), oxygen O ₂ contained in the oxidant gas supplied to the oxidant chamber (58) reacts with hydrogen ions H ⁺ and electrons e ⁻ supplied from the fuel electrode (55). Then, water H ₂ O is produced. In this way, water is generated from hydrogen and oxygen and an electromotive force is generated in the battery as a whole.

Since the electromotive force of one cell (50) is low, a plurality of cells (50) are connected in series with each other to form a solid polymer electrolyte fuel cell. For example, the solid polymer electrolyte fuel cell (5) shown in FIG. 13 has a plurality of flat unit cells (50).
And a fuel gas such as hydrogen gas is supplied to these unit cells (50) and an oxidant gas such as air is supplied to these unit cells (50) to be connected in series. It is possible to take out the electric power generated by the plurality of unit cells (50) to the outside.

In the solid polymer electrolyte fuel cell (5), each unit cell (50) has a plurality of fuel gas supply grooves (not shown) extending vertically and a plurality of oxidants extending horizontally. A gas supply groove (53) is opened. The unit cell (50) arranged at one end has a fuel gas inlet hole (51
a) is formed, the unit cell (50) arranged at the other end is formed with a fuel gas outlet hole (52a), and a plurality of other unit cells except the unit cells at these ends ( A fuel gas supply through-hole (51) and a fuel gas exhausting through-hole (52) are formed in each of 50). Then, a plurality of unit cells (5
By stacking (0) on each other, the fuel gas inlet hole (51a) and the plurality of fuel gas supply through holes (51) communicate with each other to form one fuel gas supply path,
A plurality of fuel gas discharge through holes (52) and fuel gas outlet holes (52
and a) communicate with each other to form one fuel gas discharge path.

Further, the solid polymer electrolyte fuel cell (5) is
An oxidant gas supply manifold (6) for covering the exposed side surfaces of the plurality of oxidant gas supply grooves (53) and supplying an oxidant gas to these oxidant gas supply grooves (53) is provided. . The oxidant gas supply manifold (6) is, for example, opened downward and is opened toward the side surface,
The air taken in through the lower opening is fed into the plurality of oxidant gas supply grooves (53).

In the solid polymer electrolyte fuel cell (5), the fuel gas is supplied to the fuel gas inlet hole (51a) as indicated by a solid arrow in the figure, and passes through the fuel gas supply passage to each unit. It is distributed to a plurality of fuel gas supply grooves formed in the cell (50) and is used for power generation reaction in the process of flowing downward in each fuel gas supply groove. On the other hand, the oxidant gas is taken in through the lower opening of the oxidant gas supply manifold (6) and fed into the oxidant gas supply groove (53) through the side opening as shown by the broken line arrow in the figure. , Each oxidant gas supply groove (53)
It is used for power generation reaction in the process of flowing.

14 and 15 show a specific structure of a unit cell (10) composed of a laminate of a plurality of plate-shaped members. The oxidant electrode (12) is arranged so as to cover one surface of the solid polymer electrolyte membrane (11), and the oxidant electrode (1
The oxidant electrode side conductive plate (14) in which a plurality of oxidant gas supply grooves (19) are provided so as to cover the surface of 2) is arranged, and further the oxidant electrode side conductive plate (14) A conductive gas separator (16) is arranged outside. Also, solid polymer electrolyte membrane
A fuel electrode (13) is arranged so as to cover the other surface of (11), and a plurality of fuel gas supply grooves (18) are provided so as to cover the surface of the fuel electrode (13). A side conductive plate (17) is arranged.

In the unit cell (10), the oxidant gas (33) is fed into the oxidant gas supply groove (19) of the oxidant electrode side conductive plate (14) and the fuel electrode side conductive plate is also fed.
The fuel gas (31) is fed into the fuel gas supply groove (18) of (17). As a result, in the fuel electrode (13), hydrogen contained in the fuel gas (31) flowing through the fuel gas supply groove (18) is decomposed into hydrogen ions and electrons, and the hydrogen ions are solid polymer electrolyte membrane (11). It moves in the form of hydrogen ions toward the oxidant electrode (12). On the other hand, in the oxidant electrode (12), oxygen contained in the oxidant gas (33) flowing through the oxidant gas supply groove (19) reacts with hydrogen ions and electrons supplied from the fuel electrode (13). Water is produced.

By the way, a typical solid polymer electrolyte membrane adopted in a solid polymer electrolyte fuel cell is a cation exchange membrane such as perfluorocarbon sulfonic acid.
In order to permeate hydrogen ions, water for wetting the solid polymer electrolyte membrane and water for hydration into hydrogen ions called mobile water are necessary.

The water required for wetting the solid polymer electrolyte membrane tends to be insufficient with only the water generated by the electrode reaction (produced water), so the shortage is covered by external supply. The most commonly used method is to humidify hydrogen, which is a fuel gas, and the supplied moisture permeates the gas diffusion layer of the fuel electrode and is transported to the surface of the catalyst layer or solid polymer electrolyte membrane. .

The most commonly used gas diffusion layer is a carbon conductive porous body represented by carbon paper. Since the pore diameter of the conductive porous body is approximately several to several tens of microns, water exhibits higher permeability in the water vapor state than in the liquid state. Therefore, steam is the most desirable form of water. However, it is necessary to perform a water repellent treatment with a fluororesin or the like so that the pores of the carbon paper do not become clogged with water. Fluorine resin exhibits water repellency even if added in a small amount, but the water repellency tends to decrease during operation of the fuel cell, so from the viewpoint of durability, add as much fluorine resin as possible. It is advantageous to do

Further, in the solid polymer electrolyte fuel cell, it is necessary to maintain the temperature within 130 ° C., which is the optimum operating temperature range, but since the unit cell generates heat during power generation, the cell module is cooled. The unit cell is kept in the optimum operating temperature range by supplying water for use. The method of supplying water to the fuel cell is classified into an external humidification method and an internal humidification method. In the external humidification method, the water required for wetting the solid polymer electrolyte membrane is vaporized outside the cell and supplied as water vapor into the cell. Further, the cooling water for controlling the cell temperature is supplied to the fuel cell module in a liquid state separately from the humidifying water. For example, the temperature of the unit cell is controlled by interposing cooling plates at a plurality of positions of the battery module and supplying cooling water to the cooling plates. On the other hand, in the internal humidification method, the water (humidification water) necessary for wetting the solid polymer electrolyte membrane and the electrode reaction is supplied in a liquid state inside the module, and part of it is vaporized by the heat of the module. Then, it becomes steam and is used for humidifying the gas. Further, the water supplied to the inside of the module is also used as cooling water for controlling the battery temperature. That is, in the internal humidifying system, the humidifying water plays two roles of humidifying gas and cooling the battery.

In the internal humidification type fuel cell, since the humidifying water is supplied into the cell as a liquid, it is not necessary to install a device for heating the humidifying water outside the cell, and an inexpensive and compact system is constructed. You can Also, the humidification water is mainly used by circulating it, and the humidification water discharged through the module contains a large amount of steam, but is cooled outside the module and returned to the liquid, and the liquid pump returns to the module again. Supplied.

[0016]

However, in the fuel cell, the temperature of the fuel cell is gradually increased by heat exchange in the process in which the cooling water supplied to the cell module passes through the inside of the cell module, regardless of the humidification method. For example, in a fuel cell in which cooling water inlets are provided at both ends of the cell module, the cells near the inlets, that is, the cells located at both ends in the cell stacking direction have the lowest temperature, The highest temperature in the cell of
A temperature distribution as shown in FIG. In particular, in an internal humidification type fuel cell, part of the humidification water is vaporized inside the cells, so the amount of heat taken by the cells located at the end in the stacking direction is larger than in the external humidification type, and the temperature distribution is It is easy to occur. Further, in the fuel cell of the external humidification system, the unit cell adjacent to the cooling plate has the lowest temperature, and the unit cell far from the cooling plate has the highest temperature.

In a battery module having such a temperature distribution, in a cell having a lowered temperature, the partial pressure of water vapor is reduced and the amount of water vapor is reduced, resulting in insufficient humidification and deterioration in performance. . When the performance degradation occurs in some cells in the module, this effect also affects other cells, causing a voltage reduction in the entire module. For example, when the fuel cell module is operating at rated power (the product of voltage and current is constant) and a voltage drop occurs in some cells, an increase in current occurs to compensate for this voltage drop,
As a result, the deterioration of the entire module is accelerated.

In order to solve such a problem, heat generating resistors are attached to both ends of the module having the lowest temperature, or current collecting plates provided at both ends of the module are used as the heat generating resistors. A fuel cell has been proposed in which the temperature drop at both ends of the module is suppressed (Japanese Patent Application Laid-Open No. 8-
167424). However, not only does the device configuration become complicated due to the provision of the heating resistor, but also a sufficient amount of heat cannot be obtained depending on the usage situation such as when the output current of the battery is small, and a sufficient temperature distribution reduction effect cannot be obtained. There was a problem.

Therefore, an object of the present invention is to solve the problem of insufficient humidification due to the temperature distribution generated in the battery module without equipping a special device such as a heating resistor, and having a simple structure. It is intended to provide a polymer electrolyte fuel cell.

[0020]

In the solid polymer electrolyte fuel cell according to the present invention, a plurality of unit cells (2) are stacked to form an integral fuel cell module (1), and the fuel cell module ( A channel of a cooling medium for cooling the unit cell (2) is formed in the inside of 1), and at least one unit cell (2a) closest to the inlet of the channel is formed.
Is set to be lower in water repellency of the fuel electrode (24) than that of the other unit cells (2). In the internal humidification type fuel cell, since the humidifying water serves as the cooling medium, the unit cell (2a) closest to the inlet of the humidifying water supply channel is set to have a lower water repellency than the other unit cells (2). To be done. Further, in an external humidification type fuel cell in which a cooling medium (cooling water) flow path is formed by a cooling plate etc. to cool the unit cell, the unit cell closest to the inlet of the cooling medium flow path such as the cooling plate etc. (2
The water repellency of a) is set lower than that of the other unit cells (2).

In the solid polymer electrolyte fuel cell of the present invention, the unit cell (2
a), eg a unit cell located at the end of the module
At (2a), the temperature becomes the lowest and the amount of water vapor generated becomes smaller, but the water repellency of the fuel electrode (24) constituting the unit cell (2a) is higher than that of the other unit cell (2). Since the water vapor generated in the unit cell (2a) is not repelled violently, the water vapor smoothly moves in the fuel electrode (24). As a result, sufficient humidification is also performed in the unit cell (2a). Since the amount of water vapor generated in the unit cell (2a) is small, even if the water repellency of the fuel electrode (24) is reduced, there is no risk of water pores clogging the pores of the gas diffusion layer.

In a specific construction, the at least one unit cell (2a) is set to have a lower water repellency of the gas diffusion layer of the fuel electrode (24) than the other unit cells (2).
As a result, in the unit cell (2a), the generated water vapor easily moves in the gas diffusion layer and is supplied to the catalyst layer.

Specifically, the at least one unit cell (2a) is formed in a smaller amount than the other unit cells (2) in the amount of fluororesin added to the gas diffusion layer of the fuel electrode (24). As a result, the water repellency of the gas diffusion layer of the fuel electrode (24) forming the at least one unit cell (2a) can be set lower than the water repellency of the other unit cell (2). As the fluororesin, polytetrafluoroethylene, tetrafluoroethylene hexafluoropropylene copolymer, tetrafluoroethylene ethylene polymer, tetrafluoroethylene hexafluoroalkyl vinyl ether copolymer, or a mixture thereof may be adopted. I can.

More specifically, the addition amount of the fluororesin to the gas diffusion layer of the fuel electrode (24) constituting the at least one unit cell (2a) is the same as that of the other unit cell (2). On the other hand, the weight ratio is set to 0.8 or less. As a result, the movement of water vapor in the gas diffusion layer of the fuel electrode (24) forming the unit cell (2a) becomes sufficiently smooth, and a high humidification effect can be obtained.

The at least one unit cell (2a)
The addition amount of the fluororesin to the gas diffusion layer of the fuel electrode (24) constituting the above is set to 5 parts by weight or more. As a result, the water repellency of the gas diffusion layer of the fuel electrode (24) forming the unit cell (2a) can be maintained at the necessary minimum and the clogging of the pores of the gas diffusion layer can be prevented.

In another specific configuration, the at least one unit cell (2a) is set to have a lower water repellency of the catalyst layer of the fuel electrode (24) than the other unit cells (2). As a result, in the unit cell (2a), the generated water vapor easily moves in the catalyst layer and is supplied to the solid polymer electrolyte membrane.

Specifically, the at least one unit cell (2a) is formed in a smaller amount than the other unit cells (2) in the amount of the fluororesin added to the catalyst layer of the fuel electrode (24). Thereby, the at least one unit cell
The water repellency of the catalyst layer of the fuel electrode (24) constituting (2a) can be set lower than the water repellency of the other unit cell (2). Incidentally, as the fluororesin, polytetrafluoroethylene, tetrafluoroethylene hexafluoropropylene copolymer, tetrafluoroethylene ethylene polymer,
A tetrafluoroethylene hexafluoroalkyl vinyl ether copolymer or a mixture thereof can be adopted.

More specifically, the addition amount of the fluororesin to the catalyst layer of the fuel electrode (24) forming the at least one unit cell (2a) is the same as that of the other unit cell (2). The weight ratio is set to 0.8 or less. As a result, the movement of water vapor in the catalyst layer of the fuel electrode (24) constituting the unit cell (2a) becomes sufficiently smooth and a high humidifying effect can be obtained.

The at least one unit cell (2a)
The addition amount of the fluororesin to the catalyst layer of the fuel electrode (24) constituting the above is set to 2 parts by weight or more. As a result, the water repellency of the catalyst layer of the fuel electrode (24) forming the unit cell (2a) can be maintained to a necessary minimum and water can be prevented from staying in the catalyst layer. Therefore, the gas flow is not obstructed.

The present invention is highly effective especially in an internal humidification type fuel cell. Further, when the solid polymer electrolyte membrane (22) constituting the unit cell (2) is formed of a polymer membrane of any of perfluorocarbon sulfonic acid type, polystyrene divinylbenzene sulfonic acid type and phenol formaldehyde type, The present invention is effective because sufficient wetting is necessary for the polymer film to exhibit ionic conductivity.

[0031]

EFFECTS OF THE INVENTION According to the solid polymer electrolyte fuel cell of the present invention, the module has a simple structure in which the water repellency of the unit cell is adjusted without equipping a special device such as a heating resistor. Sufficient humidification can be performed throughout.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment in which the present invention is applied to an internal wettable solid polymer electrolyte fuel cell will be specifically described with reference to the drawings. The solid polymer electrolyte fuel cell according to the present invention comprises a plurality of unit cells as shown in FIG.
(2) is laminated, and the laminated body is made into a pair of current collecting plates (7)
It is clamped from both sides by (7), and the fastening plates are on both sides.
(6) By arranging (6) and fastening both fastening plates (6) and (6) with a plurality of fastening bolts (61) and fastening nuts (62), an integrated fuel cell module (1) is constructed. is doing.

Each fastening plate (6) has a fuel gas at the upper end.
(Hydrogen gas) and two fuel gas supply pipes (63) (63) for supplying humidification water to each unit cell (2) are connected, and each unit cell (2) is attached to the lower end. Two unreacted gas discharge pipes (64) (64) for discharging the unreacted gas that has passed are connected. In addition, a pair of electrode terminals (71) (71) for projecting the generated power of the fuel cell module (1) to the outside is provided on the pair of current collecting plates (7) (7). A manifold (not shown) for supplying air as an oxidant gas is provided on the back side of the fuel cell module (1) shown in FIG.

As shown in FIG. 2, each unit cell (2) has a structure in which a cell unit (21) is sandwiched by conductive plates (3) and (3) from both sides. )
An insulating sheet (25) is interposed between (3) to provide electrical insulation and gas seal between the conductive plates (3) and (3).

The conductive plate (3) is made of a conductive material such as carbon or metal. As shown in FIGS. 2 and 4 to 7, the fuel gas supply pipe (63) ( A pair of left and right supply-side through holes (34) (34) connected to (63) are opened, and a pair of left and right discharge-side through holes (64) (64) connected to the unreacted gas discharge pipes (64) (64) are formed at the lower end. 35) (35) has been opened.
The pair of left and right supply side through holes (34) (34) are conductive plates.
The pair of left and right discharge side through holes (35) and (35), which are connected to each other through the collecting channel (36) that horizontally extends in the inside (3), are the collecting channels that horizontally extend in the conductive plate (3). They are connected to each other via (37).

Further, in the conductive plate (3), a recess (31) for engaging the fuel electrode (24) is formed on the surface of the cell unit (21) facing the fuel electrode (24), and A plurality of grooves (32) for flowing a fuel gas (hydrogen gas) in a vertical direction are provided in parallel with each other at the bottom of the recess (31), and both ends of each groove (32) are respectively formed. , Which are connected to the branch flow paths (38) and (39) extending vertically in the conductive plate (3), and these branch flow paths (3
8) (39) is connected to the collecting channel (36) (37)

On the other hand, on the surface of the cell unit (21) facing the oxidant electrode (23), a recess (41) with which the oxidant electrode (23) is engaged is formed, and the recess (41) of the recess (41) is formed. A plurality of grooves (42) for flowing an oxidant gas (air) in a horizontal direction are provided in the bottom portion in parallel with each other, and both ends of each groove (42) are electrically conductive plate (3). ) Is connected to the flow paths (43) (43) extending in the left and right, and these flow paths (43) are open at both end surfaces of the conductive plate (3). Further, on both sides of the conductive plate (3), the recesses (31) and (41) are surrounded, and the O-ring (2
Grooves (33) (40) for fitting 8) are recessed.

As shown in FIG. 3, the cell unit (21) has an oxidizer electrode (23) and a fuel electrode (2) on both sides of a solid polymer electrolyte membrane (22).
It is configured by deploying 4). Where the solid polymer electrolyte membrane
The (22) is formed to have a larger outer dimension than the oxidizer electrode (23) and the fuel electrode (24). Each of the oxidant electrode (23) and the fuel electrode (24) is formed by forming a catalyst layer having an electrocatalytic action on an electrode base material. The electrode substrate is generally produced by adding a water-repellent substance such as a fluororesin to a conductive porous material such as carbon paper, and exerts a function as a gas diffusion layer to prevent a fuel gas or a gas. At the same time as supplying and discharging oxidant gas and water vapor, it also exhibits the function of collecting electricity. Generally, the catalyst layer is prepared by mixing a catalyst containing platinum fine particles and a water-repellent substance such as a fluororesin, and mixing this with a solvent to form a paste or ink, which is then opposed to the solid polymer electrolyte membrane. It is formed by coating on one side of the electrode base material to be formed.

The insulating sheet (25) is made of an insulating material such as fluororesin or rubber, has the same outer dimensions as the conductive plate (3), and has the solid polymer electrolyte of the cell unit (21). It has an opening (26) into which the membrane (22) fits. In addition, the upper and lower ends of the insulating sheet (25) are provided with four holes which match the supply side through holes (34) (34) and the discharge side through holes (35) (35) of the conductive plate (3). Through holes (27) to (27) are opened.

The current collecting plate (7) is made of a conductive material such as carbon or metal. As shown in FIG. 8, the supply side through hole () of the conductive plate (3) is formed at the upper end and the lower end. 34)
(34) and four through holes that match the discharge side through holes (35) and (35)
(72)-(72) are open. Further, the pair of electrode terminals (71) and (71) are projectingly provided on the end surface of the current collecting plate (7).

Therefore, as shown in FIG. 2, the cell unit (21) and the insulating sheet are provided between the two conductive plates (3) and (3).
By sandwiching (25), the oxidizer electrode (23) of the cell unit (21) engages with the recess (41) of the left conductive plate (3), and the fuel electrode (24) of the cell unit (21) is ) Engages with the concave portion (31) of the conductive plate (3) on the right side, and further, the peripheral portion of the solid polymer electrolyte membrane (22) is electrically conductive to the left and right via the O-rings (28) and (28). It will be pinched from both sides by the periphery of the sex plate (3) (3). In addition, the insulating sheet (25) is interposed between the left and right conductive plates (3) (3). As a result, the fuel gas flowing in the groove (32) of the right conductive plate (3) and the groove (42) of the left conductive plate (3).
At the same time as being sealed with the oxidant gas flowing through, the electrical insulation is provided between the left and right conductive plates (3). Thus, from the combination of the cell unit (21), the insulating sheet (25) and the conductive plate (3), one unit cell is obtained.
(2) is configured.

A plurality of unit cells (2) are laminated as shown in FIG.
The current collecting plates (7) and (7) are arranged on both sides of the fastening plates (6) and (6), and the fastening plates (6) and (6) are arranged on both sides thereof. ) And a fastening nut (62) to assemble the integrated fuel cell module (1). In the fuel cell module (1) thus assembled, the supply side through holes (34) of the plurality of fuel cell modules (1) are connected to each other, and the fuel gas supply pipe (6
3) One gas supply path connected to (63) is formed, and
The discharge side through holes (35) of the plurality of fuel cell modules (1) are connected to each other and connected to the unreacted gas discharge pipes (64) (64) 1
A book gas outlet is formed.

Therefore, when the fuel gas and the humidifying water are supplied from the fuel gas supply pipes (63) (63), the fuel gas and the humidifying water flow through the gas supply passage formed by the supply side through hole (34). , From the supply-side through hole (34) of each unit cell (2) to the collecting channel (36), and further distributed into a plurality of branch channels (38) to be formed in each unit cell (2). Multiple grooves (3
It flows into 2) and is used for electrode reaction and humidification in each unit cell (2). The unreacted fuel gas and water flow into the collecting channel (37) through the plurality of branch flow channels (39), and further pass through the gas discharge path formed by the discharge side through hole (35) to unreact gas. It will be discharged from the discharge pipes (64) (64).

In the above fuel cell module (1),
Unit cells (2a) located at the inlet of the flow path of the humidifying water (cooling water) formed by the supply-side through holes (34) of the plurality of unit cells (2), that is, at both ends of the fuel cell module (1) (2a) is
The water repellency of the fuel electrode (24) is set lower than that of the other unit cells (2). Specifically, the amount of fluororesin to be added to the electrode base material (gas diffusion layer) that constitutes the fuel electrode (24) and / or the catalyst layer on the electrode base material is changed depending on the position of the unit cell (2). By doing so, the water repellency of the fuel electrode (24) is adjusted.

[0045]

EXAMPLES The results of actually producing the fuel cell module (1) of the present invention and comparing it with a conventional fuel cell module will be described.

[0046]Example 1 The cell unit used in the fuel cell module of the present embodiment.
Was manufactured as follows. Area 100 cm^TwoCarbo
Commercially available fluororesin dispersion (polytetrafluoroethylene)
Luoroethylene (PTFE) dispersion solution) and heat treatment
Carbon paper weight: 100
On the other hand, fluororesin weight: 50
In addition, carbon powder supporting platinum fine particles, perfluorocarbon
Carbonic acid alcohol solution and carbon powder
To prepare a slurry containing 25 parts by weight of fluororesin
After that, the amount of platinum carried is about 1 mg / cm^TwoAs before
Apply the slurry on the electrode substrate and dry it.
To produce the oxidizer electrode (23) and the fuel electrode (24).
It was These oxidizer electrode (23) and fuel electrode (24) are
Solid polymer composed of orocarbon sulfonic acid polymer film
Contact both sides of the electrolyte membrane (22) by a method such as hot pressing.
Then, a cell unit (21) was produced.

However, the unit cell located at the end of the module
For the cell unit (21) used in (2a),
In the preparation of (24), the amount of fluororesin added to the carbon paper was 20 parts by weight. As a result, the addition amount of the fluororesin in the diffusion layer of the fuel electrode (24) used in the unit cell (2a) is the same as the addition amount of the fluororesin in the diffusion layer of the fuel electrode (24) used in another unit cell (2). For quantity,
The ratio is 0.4.

The fuel cell module of Example 1 was assembled by setting the number of stacked unit cells (2) thus manufactured to 30.

[0049]Comparative Example 1 All the unit cells of the fuel cell module are the same as those in the first embodiment.
It is composed of the same unit cell as the unit cell (2) in the center.
A fuel cell module as described above was assembled to obtain Comparative Example 1.

[0050]Performance comparison Targeting the fuel cell modules of Example 1 and Comparative Example 1
The fuel gas supply pipe of each fuel cell module (63) (63)
To this, supply 300 cc / min of humidifying water and hydrogen, and
A rated operation with a joule output of 0.5 kW was performed. In addition,
The amount of humidifying water to be supplied depends on factors such as cell configuration and output current.
It is desirable to decide as appropriate in consideration of the circumstances.

FIG. 10 shows changes with time in module voltage in Example 1 and Comparative Example 1. As shown in the figure, in Example 1, the decrease in voltage with time is smaller than in Comparative Example 1. In Comparative Example 1, since the temperature of the unit cells at both ends is low, the vapor pressure of water is low, and the amount of water that permeates the gas expansion layer of the fuel electrode and reaches the catalyst layer is small. In contrast to the lack of water required for the unit cell to reduce the reactivity of the unit cell, in Example 1, the water repellency of the gas diffusion layer of the fuel electrode forming the unit cell at the module end is suppressed. This is because the amount of water reaching the catalyst layer is increased and the decrease in reactivity of the unit cell is suppressed.

[0052]Example 2 In this embodiment, it should be attached to the unit cell at the end of the module.
The effective range of the difference in water repellency was examined. Implementation
In Example 1, the fuel forming the cells at the end of the module
Change the amount of fluororesin added to the gas diffusion layer of the electrode to another value.
The ratio is 0.4 with respect to the same amount of
In the embodiment, regarding the cells at the end of the module,
The amount of fluororesin added to the gas diffusion layer is 2% each.
Parts (ratio 0.04), 5 parts by weight (ratio 0.1), 40 parts by weight
(Ratio 0.8), 45 parts by weight (Ratio 0.9) 4 types of fuel
Rechargeable battery modules (Examples a to d) were produced.

FIG. 11 shows changes in the module voltage when the same operation as in Example 1 is performed. As is clear from this graph, in Example b (ratio 0.1), Example c (ratio 0.8), and Example 1 (ratio 0.4), the decrease in module voltage over time was significantly reduced. And a great effect is obtained.

However, in Example d (ratio 0.9),
Since the water repellency becomes excessive and the amount of water that can reach the catalyst layer of the fuel electrode decreases, the effect of suppressing the decrease in reactivity becomes relatively small. Therefore, the amount of fluororesin added to the gas diffusion layer of the fuel electrode that constitutes the cell at the end of the module is
It can be said that it is preferable to set the ratio to 0.8 or less with respect to the same addition amount of other cells.

In Example a (ratio 0.04),
Since the absolute amount of the added fluororesin is as small as 2 parts by weight, the water repellency becomes too small, which causes the pores of the gas diffusion layer to be clogged with water and the gas diffusivity of the fuel electrode to decrease, so that the reaction The effect of suppressing the deterioration of sex was relatively small. Therefore, it can be said that the addition amount of the fluororesin to the gas diffusion layer of the fuel electrode forming the cell at the end of the module is preferably 5 parts by weight or more in absolute amount.

[0056]Example 3 In this embodiment, the water repellency is adjusted by using the diffusion layer.
Therefore, the effect of the catalyst layer was examined.
In this example, the module end manufactured in Example 1 was used.
To the catalyst layer of the fuel electrode that constitutes the unit cell (2a)
The amount of the base resin is 1 part by weight, 2 parts by weight with respect to the carbon powder,
Except for 10 parts, 20 parts and 23 parts by weight
In the same manner as in Example 1, five types of fuel with 30 laminated cells were used.
A battery module (Examples e, f, g, h, i) was prepared.
It was

In these fuel cell modules, the amount of the fluororesin added to the catalyst layer of the fuel electrode forming the unit cell (2a) at the module end is different from that of the other unit cells. 0.04, 0.08, 0.0.
The ratio is 4, 0.8 and 0.92 (see Table 1).

[0058]

[Table 1]

FIG. 12 shows changes in the module voltage when the same operation as in the first embodiment is performed. As is apparent from this graph, in Example f (ratio 0.08), Example g (ratio 0.4), and Example h (ratio 0.8), the decrease in module voltage with time is significantly reduced. And a great effect is obtained.

However, in Example i (ratio 0.92), the water repellency becomes excessive and the amount of water that can reach the catalyst layer of the fuel electrode decreases, so that the effect of suppressing the decrease in reactivity is relatively high. It became small. Therefore, the amount of fluororesin added to the catalyst layer of the fuel electrode that constitutes the cell at the end of the module is
It can be said that it is preferable to set the ratio to 0.8 or less with respect to the same addition amount of other cells.

In Example e (ratio 0.04),
Since the absolute amount of the added fluororesin is as small as 1 part by weight, the water repellency becomes too small, which causes water to stay in the catalyst layer and hinders the gas flow. It became small. Therefore, it can be said that the addition amount of the fluororesin to the catalyst layer of the fuel electrode forming the cell at the end of the module is preferably 2 parts by weight or more in absolute amount.

The solid polymer electrolyte fuel cell according to the present invention is a solid polymer electrolyte membrane, for example, perfluorocarbon sulfonic acid type, polystyrene divinylbenze sulfonic acid type, phenol formaldehyde type, which has a great influence on the cell performance in the humidified state. It is particularly effective in a fuel cell using a solid polymer electrolyte membrane such as, and is also effective in an internal humidification type fuel cell in which the temperature distribution of the module tends to be large.

In Example 3, the amount of the fluororesin added was adjusted in order to control the water repellency of the catalyst layer. However, the present invention is not limited to this, and the nature of the carbon powder carrying the catalyst is not limited to this. A method of controlling the water repellency can be adopted. In this case, the carbon powder has different water repellency depending on its shape and surface condition such as surface area and degree of graphitization. Therefore, the characteristics of the carbon powder used in the catalyst layer are different between the cell at the module end and the cell at the module center. The water repellency may be made different by using the above.

Although PTFE is used as the fluororesin in Examples 1 to 3, the invention is not limited to this.
Tetrafluoroethylene hexafluoropropylene copolymer (FEP), tetrafluoroethylene ethylene polymer
(ETFE), tetrafluoroethylene hexafluoroalkyl vinyl ether copolymer (PFA) and the like can be used for the same production.

The number of unit cells (2a) at the end of the module whose water repellency is to be adjusted is not limited to one, and the water repellency can be adjusted for a plurality of unit cells near the end of the module. It is preferable to set the number according to the number of stacked layers and other conditions. In this case, the water repellency of the plurality of unit cells can be given a distribution in accordance with the temperature distribution shown in FIG. 9, for example.

The present invention can also be implemented in an internal humidification type or external humidification type fuel cell in which a cooling water flow path is formed by a cooling plate or the like to cool the unit cells. The water repellency of the unit cell (2a) closest to the inlet of the cooling water flow path such as the plate is set to the other unit cell
Set lower than (2). Furthermore, in the external humidification type fuel cell, oil, organic liquid or the like can be used as the cooling medium in addition to water.

[Brief description of drawings]

FIG. 1 is a side view showing a solid polymer electrolyte fuel cell module according to the present invention.

FIG. 2 is a front view of the unit cell in a disassembled state.

FIG. 3 is an exploded perspective view of a cell unit and an insulating sheet.

FIG. 4 is a perspective view showing a surface of a conductive plate facing an oxidant electrode.

FIG. 5 is a perspective view showing a surface of a conductive plate facing a fuel electrode.

FIG. 6 is a front view showing a surface of a conductive plate facing an oxidant electrode.

FIG. 7 is a front view showing a surface of a conductive plate facing a fuel electrode.

FIG. 8 is a front view of a current collector plate.

FIG. 9 is a graph showing a temperature distribution of a plurality of cells forming a fuel cell module.

FIG. 10 is a graph showing a decrease over time in module voltage in Example 1 and Comparative Example 1.

11 is a graph showing the time-dependent decrease in module voltage in Example 1, a to d and Comparative Example 1. FIG.

FIG. 12 is a graph showing a decrease with time in module voltage in Examples e to i and Comparative Example 1.

FIG. 13 is a perspective view showing an appearance of a conventional solid polymer electrolyte fuel cell module.

FIG. 14 is a cross-sectional view showing a main part of a unit cell constituting the solid polymer electrolyte fuel cell module.

FIG. 15 is an exploded perspective view of the unit cell.

FIG. 16 is a diagram illustrating a power generation principle of a solid polymer electrolyte fuel cell.

[Explanation of symbols]

(1) Fuel cell module (2) Unit cell (21) Cell unit (22) Solid polymer electrolyte membrane (23) Oxidizer pole (24) Fuel electrode (25) Insulation sheet (3) Conductive plate (34) Supply side through hole (35) Discharge side through hole (63) Fuel gas supply pipe (64) Unreacted gas exhaust pipe

Continuation of front page (56) References JP-A-9-283153 (JP, A) JP-A-5-251086 (JP, A) JP-A-58-163173 (JP, A) JP-A-8-167424 (JP , A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01M 8/00-8/24 H01M 4/86-4/98

Claims (9)

(57) [Claims] 1. A unitary fuel cell module (1) is formed by stacking a plurality of unit cells (2), and each unit cell (2) comprises:
Between the fuel electrode (24) and the oxidizer electrode (23), the solid polymer electrolyte membrane (2
2) is interposed, the fuel gas is supplied to the fuel electrode (24) and the oxidant gas is supplied to the oxidant electrode (23) to generate electric power generated by each unit cell (2). In the solid polymer electrolyte fuel cell capable of taking out the air, a flow path of a cooling medium for cooling the unit cell (2) is formed inside the fuel cell module (1). And at least one unit cell (2a) closest to the inlet of the flow path
Is a polymer electrolyte fuel cell in which the water repellency of the fuel electrode (24) is set lower than that of the other unit cells (2). 2. The solid polymer electrolyte membrane (2
2) A catalyst layer is formed in a region contacting with 2), and a gas diffusion layer is formed in a region opposite to the catalyst layer.
The solid polymer electrolyte fuel cell according to claim 1, wherein one unit cell (2a) is set to have a lower water repellency of the gas diffusion layer of the fuel electrode (24) than the other unit cells (2). 3. The at least one unit cell (2a)
The solid polymer electrolyte fuel cell according to claim 2, wherein the amount of the fluororesin added to the gas diffusion layer of the fuel electrode (24) is smaller than that of the other unit cells (2). 4. The addition amount of the fluororesin to the gas diffusion layer of the fuel electrode (24) constituting the at least one unit cell (2a) is 0 with respect to the same addition amount of the other unit cell (2). .
The solid polymer electrolyte fuel cell according to claim 3, which has a weight ratio of 8 or less. 5. The addition amount of the fluororesin to the gas diffusion layer of the fuel electrode (24) constituting the at least one unit cell (2a) is 5 parts by weight or more, according to claim 3 or 4. Solid polymer electrolyte fuel cell. 6. The solid polymer electrolyte membrane (2) is provided on the fuel electrode (24).
2) A catalyst layer is formed in a region contacting with 2), and a gas diffusion layer is formed in a region opposite to the catalyst layer.
The solid polymer electrolyte fuel cell according to claim 1, wherein one unit cell (2a) is set to have a lower water repellency of the catalyst layer of the fuel electrode (24) than the other unit cells (2). 7. The at least one unit cell (2a)
The solid polymer electrolyte fuel cell according to claim 6, wherein the amount of the fluororesin added to the catalyst layer of the fuel electrode (24) is smaller than that of the other unit cells (2). 8. The addition amount of the fluororesin to the catalyst layer of the fuel electrode (24) constituting the at least one unit cell (2a) is less than that of the other unit cells (2). The solid polymer electrolyte fuel cell according to claim 7, which has a weight ratio of 8 or less. 9. The solid according to claim 7, wherein the amount of the fluororesin added to the catalyst layer of the fuel electrode (24) constituting the at least one unit cell (2a) is 2 parts by weight or more. Polymer electrolyte fuel cell.